I have to agree with almost everything elitemob says here. You definitely need 2Gb of RAM and the first thing you should do is set up an administrator account and turn the User Account Control (UAC) off. I know it's only a couple of clicks to confirm any action but after a while this will drive you bonkers. It did with me anyway so I just turned it off.

I've had Vista for around 3 months now and it hasn't crashed a single time. Also, PT, PAHud and all the Poker Site software work absolutely fine.

BTW, I don't think turning the UAC off makes the computer much less secure. If you are logged on as a user other than administrator, where you used to get a prompt for the administrator password, it will now just refuse to perform the action. The only way it is less secure, is when you are logged on as administrator, it will no longer give you the warning prompt. But if you are the administrator you should know what you are doing anyway.