Use MS Paint which should come with your copy of Windows. Or try Gale Graphics or GIMP, and if you're not poor, Photoshop CS 2 or Paint Shop Pro 9. Oh and if you can't find a download link, I suggest using a brand new search engine that hasn't been around that long and that nobody knows about, called
Google. Oh boy I sure do hope they get publicity.
Next time, read the [CENSORED]ing FAQs.
Edit: Okay, if you've tried them then they should work, eh? Maybe you mean "why can't I make nice looking mods with MS Paint?" Well, in that case, it's not anybody else's but your fault that you're terrible with pixels. End.