Vista - applying updates

i have a VB6 application that periodically checks for version updates on our
servers over the internet. if a new version is found, it is downloaded to
the %temp% directory on the client's machine, and the current process is
stopped while the new executable is copied into the program files directory
overwriting the old version. the application is then started up again.
this all works fine on XP but due to Vista's new security settings, the
process of copying the new executable into the progaram files directory is
blocked even when im logged in as admin, which causes the update to fail.

the application is launched upon startup via a shortcut created during
install in the startup directory. if i manually set the privilege level in
the compatibiliy settings of the shortcut to run as administrator the update
works fine, but i can't find a way to do this programmatically. we are
currently using wix to generate a .msi file which performs the initial
installation routine. do i need to create a new install package in order to
make this work? can someone point me in the right direction here? it seems
like this should be a fairly simple task but i've spent a lot of time on
this to no avail. am i doing something fundamentally wrong? i've done
quite a bit of research on this topic but can't seem to find a good example
that applies specifically to VB6 applications.

any help you can offer will be much appreciated,

thanks!