Welcome to the forums!
Unfortunately, your VIA P4M900
based system is extremely dated and, as such, official Windows 7 drivers are not provided through VIA's Download Page
They do however provide Windows Vista drivers which, with a little effort
, could potentially be used.
Alternately, Windows 7 should be able to obtain the latest drivers through Windows Update.
As a last resort, I have located Windows 7 drives for your IGP Here
Unfortunately, I can not vouch for the site and would only recommend trying them after all other options have been explored.