When you leave it in hibernate or sleep mode with nothing but the power lead connected, it still wakes itself up.
Im afraid I have no idea what this could be, possible some software that is running on your system may be doing it?
I still have not got full driver support for my wireless card, which drops out on me and just does not work when i return to my laptop after it has been supposedly sleeping!
Have you tried going to the manufacturers website and seeing if there are any new vista drivers available for download? are you in good signal range of the access point, I have previously had some issues with signal loss on my macbook pro because of access point placement. im asuming that you have an older laptop and when you bought it, it came with xp on it? in this case if you cant find drivers for your wireless card it may be an idea to go back to XP.
I know what you mean about, the vista slate, but vista is still no where near as stable as a Mac OS X or XP with SP3, also i can't think of a time since Feb 07 when i got vista, when i have not had some sort of problem with it, just really bugs me!
I would also agree and say that OSX is much more stable than any vershion of windows, XP or vista, but that is because OSX is designed to only work on the limited amount of apple hardware and not 1,000's Plus different hardware that runs Windows, this is one advantage of OSX. It just depends on what hardware you are using and what the driver support is like. With apple stuff the hardware/driver support is nearly always spot on, but with windows its more difficult.
Good luck with your problems, I hope you find a solution!
P.s Since usin Mac OSX I have had much less problems that I do with windows, for home users I would highle recommend macs!