I like Helton alot as a first round pick if you miss out on Pujols, ARod, and Soriano. He is an absolute offensive monster, and I think the best 1B in baseball, although some will argue Delgado or Giambi is better. He's a great guy to build your offense around. Nomar as the second pick is also solid, gives you a great SS to solidify a weak position, and Nomar will hit .330-30-120 probably.
I don't really like taking Foulke in the the third round though. He is a solid closer, but unless you can get Smoltz or Gagne, the third round is too early to reach for a closer IMO. You would have been better served getting a top notch starting pitcher or a strong outfielder here. Prior and Oswalt are great picks and give you two top 10 starting pitchers, provided Oswalt's injury isn't serious.
I also think the Castillo and Chavez picks were good because it gives you top 5 guys at the two weak positions. You are also set for closers with two elite guys in Percival and Foulke, plus Biddle, Izzy and Worrell thrown in.
Taking Loaiza and Chacon at all, and especially this early was a mistake. I think both guys have gotten lucky so far and are flukes. You probably could have gotten someone more established that has been struggling at those picks. For example, I would far rather have Freddy Garcia or Al Leiter than Chacon or Loaiza. Don't count on either of them to be more than spot starters for the rest of the year.
Your infield looks solid, and your pitching should be OK if you start Prior and Oswalt all the time and selectively start your other guys. I might consider seeing if someone is in desperate need of a decent closer and move Percival or Foulke to bring in a better #3 starter, since 5 closers might be a bit excessive anyway.
You obviously left your outfield until later in the draft, which makes it a bit weak, but it seems like you should already have enough HR and RBI production from Helton, Garciaparra, Chavez, and Juan Gone in the OF to get by. I would recommend starting Sanchez in your OF all the time because Castillo is your only other steals source, so you'll need his speed.
If you can bring in a solid #3 pitcher, you have a nice team.