All depends - usually placing ram is very simple. There's usually atleast 2 little slots that you just pop it in and it's there.
I've had computers with generic ram in them that are 8 years old and still working, just try to get low-latency ram.
*edit*OOPS! oh, and, as far as power supplies go, depending on waht you're using it for, 420 watt will probably be plenty ^^
New PC (Finished May 4, 2004)
Athlon XP 2800+
Soyo Dragon ultra Platinum KT600
1024 MB Kingston Hyper-X
120GB 7200 RPM 8MB
160GB 7200 RPM 2MB
GeForce FX5500 256MB
16x52x32x52 DVD/CDRW Combo