Ditto on the tower, as it'll just be there collecting dust while looking pretty.
I saw that same ram kit being sold for 14.99 on Boxing Day, so if you take the above advice, just keep the money you save and spend it on the next major holiday.
According to the reviews I've read (on other sites) about that keyboard set, the mouse is a battery-eating monster. The keyboard is still good though.
And about XP SP2. If you can assemble your own PC, I'm pretty sure you have some friends who can do the same. Odds are one of them has a pirated copy of XP. If you have nothing against piracy, just get it from them and turn off automatic update. You can buy tons of things with $140.