Arghh, HP
In any case that shows as out of stock, and a monitor would be extra.
Most of the big mass producers of computers can often use non standard components. They work well, but aren't easily replaced or upgraded. Also many of the manufacturer's don't supply the software but instead use restore discs which can make it difficult to adapt the PC to your specific liking. On the other hand it should work well out of the box.
If the computer's main use is likely to be gaming, then consider checking out your local computer shop. They may well be able to build you something from standard components that will outperform the big high street store offerings. You'll be looking for good graphics, a decent CPU and ideally for Vista 4 GB of RAM. You can always add more hard disc space later, so you could compromise a little on cost there, but hard discs these days are quite cheap.
Look for a 64bit version of Vista rather than 32. 64 should make better use of the modern CPU if you have enough RAM, and would be a tad more future proofed.