changing UID

[terry]

hi -

i'm running an asp.net app w/ a vb.net backbone. simply put it's a
remote filesystem browser that isn't supposed to show files the user
isn't allowed to access. the page requires authentication, but the
user running the program is always "ASPNET". this means that file
permissions aren't unique (or appropriate) to the user at this time.

anyways, if given a username is there a way that i can change the uid
and call another program? what if i'm given a password, too?

thanks!
terry