More questions than answers –
A) Domain or workgroup?
B) If domain, local or romaing profiles?
C) DNS (active directory or not)?
D) What else shares the T1 to the colocation?
E) What type documents? Plaintext or XML? PDFs or MS Office? IF office haveyou reviewed the kb article on Word and Excel problems on slow links?
Do you have a baseline profile of the connection?
As you can see the more info we have the better our answers can be.