No, it's NOT a Vista problem.
I know several people with HP 6000s and the like with the problem.
There's an enormous thread on it
here.
Basically, it goes like this:
1. The WiFi disappears.
2. Poking around with the software, restore, driver change, BIOS change, etc brings it back for a while. Lots of people post their "patent" solutions which work - but only for a while.
3. Then the WiFi disappears and doesn't reappear.
4. You spend a long time arguing with HP, who may or may not accept your machine back for repair - depending on how aggressive you get.
The cause is that the graphics chip gets so hot it melts the solder on the motherboard, which disconnects the WiFi bit on the board.
If you plug in a wireless dongle, it'll work for another month or so, then the solder further down the MoBo melts and the machine is dead.
How do I know? I have friends who bought the same machine. All of them have had the same problem.
HP will replace the motherboard. If the new motherboard has a fix (I don't know if it does), you'll be OK. Otherwise, it'll do it again.
You need to be fairly firm with HP, so that they either fix or replace your laptop. Quoting that thread above should do it.