a fast reply would be to: 1) use the flash utility provided by your board manufactor to flash the Bios. 2) Then you need an OEM-key matching the installation of Vista you are using (Home, Business, Ultimate and so on) 3) Then you need to know which SLIC info is present in the modded Bios to get the corresponding cert-file to use to get your Vista activated. Seacrh this forum for the OEM keys and certs and I'm sure you will find them including the syntax for using them in Vista. The cert is just a file that needs to be on your harddrive and have to match the SLIC info in your bios. Then you change or add (depending on if you entered an key during install) the OEM licensekey to your Vista install and after that you "import" the cert-file to switch Vista into activated mode.. This needs to be done with Admin privilages with UserAccountControl turned off.. I hope this gives you some hints on how to move further..
@ GlasgowRangers i downloaded your modded bios and had a look it has been modded for ASUS hope this helps you