Is there any way to know when prices drop in certian hardware?
Manufacturers will usually announce when price drops are going to happen, as Intel did a few weeks ago for their 45nm processors.
And when releases for new GPUs and other hardware will happen?
Just use a decent computer hardware site to keep up to date with what is going on. http://www.xbitlabs.com/
Future releases I know of:
late May-June 2008: RV770 (HD 4800 series)
July-August 2008: Nvidia GT200
Q3 2008: 45nm Phenoms
Q1 2009: Intel Nehalem