I've been really into the computer scene lately and I've built myself a couple. I got most of my stuff from NewEgg.
For the memory, corsair is testing to be one of the best right now. Will you be overclocking? I have a stick of Corsair XMS 3200-C2 (512MB), and its running@ 173 FSB at the fastest RAM timings with no problem. Performance is great.
For motherboards, I prefer Abit and Asus, but MSI should be fine.
The Enermax PSU is good. I have one of those and an Antec Tru Power 430, and both are nice.
If you're set on a P4, that's a fine chip, but I don't know that much about P4s.
The video card.... if you're not a hardcore gamer, a Ti4200 should be good. I got one of those to hold me over until they release their new line of cards next year.
A lot of this depends if you're planning on O/C'ing or not.
I learned a lot from
www.overclockers.com forum, you might want to check it out.