Hey JuMe! I had the same damn problem, since I'm also using XP Pro. After much monkeying around with BIOS's, and just going crazy, I suddenly realized the usual answer......REVERT TO AN EARLIER VERSION! So, I tried all the previous versions, and have found the GENS 1.90 will work with XP Pro. You can get 1.90 at the GENS homepage!
Can someone provide a direct link to the Gens emulator download, as i'm in school atm.. and the site u gave in the last page of this thread did not work for me.. damn governement.. thanx in advance.. Harry