As it's Basic you're getting, and will be in a shop, it may be worth putting one through its paces to get some idea. But you still won't get the full experience of what it will be like. For the record I have six Vista machines, all with 4Gb memory, and they need it. It should not really make much difference to the price. I used a Vista laptop with only 1Gb for a little while, it was hopeless, but was running Home Premium.
Woodchip does not use Vista, so his comment is uninformed. You cannot buy a computer with XP preinstalled any more. Microsoft put a stop to that on 30th June, so another uninformed comment. In the end it's up to you.