Wherever the users profiles are stored on the citrix server - give them the correct access in the "security" tab of the profile folder (full control or change - because that have to be able to read, write, and delete).
Also, I don't think that you can change the clients hard drive letters in Citrix. You only have one shot to do this and this is during the installation of Citrix. You have two choices 1. Map Server Hard drives starting with C-U and have the users hard drive map to V-Z OR 2. Have the servers hard drives map to V-Z and the clients hard drives map starting with C-U. I think that number 2 is the best way to go so the users won't get confused. We have to keep it as simple as possible!!
Also, If you have a PDC or BDC that handles all the profiles you really don't have to worry too much about the profiles on the citrix server. These are basically cached to speed up logon. FYI: If you are running low on space on the citrix server and you have a PDC that is handling the profiles - go and delete all the old profiles that are not the current day (sort by date). Just make sure that you do not delete the All Users, Profile user (if there is one), and the administrator profile. I did this and gained almost 2.5 Gig worth of space!
Like masai said - the best way to handle profiles is to have a solo server do this. Profiles take up a lot of space and can bring a server to its knees in certain circumstances.
Hope this helps!
Pinkman MCSE, CCA