jacknet,
In my experience, it pays to visit the target of your link and ask the support team if 1) they are OK with your link and 2) if they have a logo or small button they can give you to use as a link.
This way, if they do send you a button, it should be accompanied by a few words about disclaimers or trademarks, something the big boys are sometimes twitchy about.
Have fun.
M
Failing that, if you are using Windows and have a link to UD.exe somewhere (ie on your bottom Quick Launch bar, right-click on that, open properties and select change icon. This opens up a mini-menu of all the icons used by UD on your PC. Do a quick screen-grab (alt-PrintScreen) and paste it into PS, PSP or FW, whichever you use) and use that as you icon.