Firstly how long is a piece of string Lol.
I gather you mean 250GB.
You have mentioned everything that goes with it....do you mean printer etc.
What is the expected use of the computer,ie...email/internet/burning the odd cd/dvd/word etc.If so,you will get some change from your budget.
However if a system is required for photo/video editing or even gaming...we can look for something a bit more powerful.
As for Vista,yes it has a few issues but these are gradually being ironed out...not to mention why take a backward step with xp.
Ive had Vista since April,and very happy with it.