Vista - Pausing, Hesitating, Choppy behavior

Anyone with any suggestions. Please, at this point i am so disgusted I will
try just about anything. 2 months ago my hard drive went wacky, (i had a
Dell Dimension with XP), I ordered new computer from Dell. This computer is
supposed to be twice the computer my dimension was. I now have a Dell XPS
with Intel Core 2 Duo Processors etc, etc. Dell does not sell these with XP
only VISTA. Which I have come to dislike greatly. In 5 weeks I have owned
this computer, since day 1 it has not run properly.

It takes twice the time to do ANYTHING. SLOW SLOW SLOW. Anyway. Every
site that my daughter goes to AOL GAMES, MSN GAMES, GRAB.com YAHOO etc.
none of the games play correctly. The computer, its hard to explain...
hesitates, or pauses producing choppy behavior, like an old Chevy needing a
serious tune up and needing the timing set badly. Timed games like Gold
Miner Vegas will hesitate while playing causing it to go from 18 to 15
seconds (example). When you play games like Battle Phlinx (aol games) where
timing and speed is very important, forget playing, cause eveyone else is
shooting 10 stones to your 3 or 4 and when you shoot the 5th time all of a
sudden your screen is filled with stones and your out of the game. I have an
old Gateway computer purchased in 1986 on dial up that runs better and
faster. I have been online with Dell 17 times in 5 weeks and no one can
help. Anyone experiencing or WAS experiencing similar with any ideas?

thanks in advance
....desperate...