As the driver issue was a major reason cited for the failure of Vista with Microsoft and Vista taking the blame for the problems i will try to explain in depth some of the factors involved in driver availability
Microsoft does not provide any drivers directly themselves - other than those for hardware built by themselves such as Microsoft Mouse etc. and certain generic items.
The drivers included with the Operating system are provided to Microsoft by the actual hardware suppliers
The actual drivers included in the OS are determined by the hardware supplier and Microsoft based on many factors Including the age of the hardware and the number of units in the field. The space available for inclusion of drivers is limited and this makes practical sense.
It is unlikely that an older piece of hardware will be supported the same applies for an item that is not widely used.
Some manufacturers will also use the release of as an opportunity to promote the sale of new equipment by the simple fact that if drivers are unavailable the end user will need to purchase replacement hardware.
A lot of manufacturers will wait until the operating system is established in the market place before spending the time and resources (money) required to develop drivers for it
Windows 7 is not yet officially released, so it is possible that further drivers will become available as the Operating system matures.
HP is actually one of the better manufacturers when it comes to supporting their hardware. The method they use is the creation of universal drivers for older hardware which will provide access to most if not all of the functions of the device.
The universal driver for the vast majority of their laser printers is available now on the HP site and is fully Windows 7 certified.
I believe it is not included in the distribution package for the Operating system due to size constraints.
Hope this helps clarify matters.
The universal printer driver is available here ...
HP Universal Print Driver Series for Windows
Even if your printer is not specifically supported it may be that it will work with the driver - if a particular printer will not work with this driver then if you contact HP they may have an alternative driver that will work