Boy did I goof up!

I have reinstalled Windows home XP 2 times with the disk
i got from DEll cause I was having too many errors and I
had way too much trouble from d/l's like Kazaa and p-
track and crap I liked like jpeg images that stuff NOW I
have tiny free space on my disk like 9.gb s free and 37.
gb used . When I did reinstall there was message saying I
already had an operating system. Damn do I need to get a
professional to fix this or is it at ALL possible that I
can save my puter my system whatever this thing is. I
will NEVER download crap again that I do not know about.
hope someone has some patience with a newbie and can
help. michele