HP has finally released their updated all in one software packages for Windows Vista. So if you have an HP all in one device and have lost the scanner and fax functionality after upgrading to Vista, (more so for networked products) you can download it now from the HP site. It is a fairly large download (160 or so MB) so ensure you have a high speed connection.
Without this software if you had a directly connected HP all in one device you could still print and scan from Vista but you had to use the built in scanner and faxing software. This would render these devices unusable if they work networked other than basic printing.