Hidden files? maybe try a better explorer like total commander. use ccleaner to regain some of the space used by browser caches, and temp files, and junk.

Try running ChkDsk to check your drive for errors. Right-click your Drive icon/ Properties/ Tools/ Error Checking.  Try it first by not checking either box (this will run it in a quicker Read-only mode) to see if it flags any hard drive or file problems.  If it does, restart  it by ticking both boxes, and rerun it to allow it to attempt to fix any found problems.

Run the Disk Cleanup tool and use the "More Options" tab to remove all but the most recent restore point.


You don't really want Restore Points going back too far as they will more than likely uninstall all programs or settings you have changed since your "go back point" causing you more problems than it may fix.

The average restore point is 25mb+ with a "first in, first out" policy on restore points.  They contain mainly deleted or altered exe, dlls, shortcuts and a registry backup and user profile details.  They do not contain users data.

Keeping restore points for a week seems adequate.  Amount of disk space used depends on the size of your restore points.  Some restore points can be as large as 500mb after major alterations to a system (ie a new service pack or several hefty program installs).

310312 - Description of the Disk Cleanup Tool in Windows XP
http://support.microsoft.com/default.aspx?scid=kb;en-us;310312&FR=1&PA=1&SD=HSCH

Physically check your User Temp file and the C:/Windows/ Temp. Faulty programs have a habit of writing realms of data to temp files and then forgetting to delete the temp files.

Your user Temp folder can be checked by typing %temp% in the Start Menu RUN box.  This will open your Temp folder, there you can delete everything that Windows will allow you to do so.

It may be necessary to show Both Hidden and System Files, and also to uncheck "Hide known file types" in Control Panel/ Folder Options/ View, to navigate to the mentioned Temp location.

You could look at this type of software as an aid?

TreeSize Free V2.4
http://www.jam-software.com/freeware/index.shtml  

I found this and it seems to have worked.

Taken from another site:

Well, it turns out Windows Vista handles system restore a little differently than Windows XP. Whereas with XP, you could adjust how much memory system restore took up with a little slider bar, there's no visible way to adjust your system restore memory settings on Vista. And by default, Windows sets aside a hefty 15% of your hard drive.

On a 120GB hard drive, it'll take about 20 GB after a few months.

First, let's see how much storage space is currently allocated.

1. Click the start menu
2. Click on All Programs, and then Accessories
3. From the accessories menu, right click on Command Prompt and select "run as administrator"
4. Type "vssadmin list shadowstorage" into the command prompt
5. The results should tell you the amount of storage used and the maximum amount alloted

If you're not happy with those numbers, here's how to resize them. Keep in mind, you will lose some older system restore points when you do this.

1. Repeat steps 1-3 to get bring up the Command Prompt
2. Type "vssadmin Resize ShadowStorage /For=[your hard disk]: /On=[your hard disk]: /MaxSize=[how much space you want to allocate]"
3. For example: "vssadmin Resize ShadowStorage /For=C: /On=C: /MaxSize=2GB"
4. You should get a message saying Successfully resized the shadow copy storage association, and you should have more free space on your hard drive.

So, all of that was from System Restore?  I highly doubt it.

My guess is that may be some of it, but that you also have a fair amount of "stuff" under your documents, pictures, app data perhaps, that sort of thing.  And if you don't have "show hidden files" checked, you won't see all of that, when you're just searching through "Computer" or Windows Explorer.

Also, you could check to make sure all the temp files are cleaned out.  CCleaner would be an excellent choice of a 3rd party app to help here.

Another thing to look at is do you have any big programs installed?  Adobe Creative Software is typically fairly large.  Many games are flat huge nowadays.

Video files is another thing.  Video files can be easily the largest individual files on a system, if you have anything there.

ISO images - if you've downloaded any ISO images, files used to burn strait to disk - Linux distros, or anything else, those quickly take up a lot of space.

a large MP3 collection can also take up a lot of space.


 

Oh, another possibility.  Log files.  It may sound silly, but some applications will keep HUGE log files if you let them.  If the Program Files folder seems way too big, then I'd check around in there.

All told, it may not just be one issue, but rather multiple issues if you don't know for sure what is taking up all your space.

You said you tried the quoted instructions.  What were your results?  How much space did you clear up?

Windows Vista shouldn't take more than 20GB by itself, could expand to maybe 30 GB with temp files and the like.

The Program Files folder for most people won't be more than a few Gigabytes... 10 or 20GB for a pretty heavily loaded system, applications installed - wise.

So, that would only be 50GB tops before your Program Data folder, system logs, and user files.  The user files are under c:/users/yourname  or c:/users/public... I'd check any folders there.