> If they do not agree then the will not be able to login
You will find it rather tricky to get a VB program to run before the user logs in.
The registry, however, contains two setting that allow you to modify the login dialog, which would allow you to display a legal notice and warning (normal caveats about how you can render your PC inoperable if you don't know what you are doing apply):
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Then add or modify the following values:
LegalNoticeCaption REG_SZ Dialog Caption
LegalNoticeText REG_SZ Dialog Message