so it seems my cl settings are 6-6-6-18. i have no idea what sort of performance difference this makes from the preferrred 4-4-4-12. is it night and day difference or is it 5% extra performance for those who have the time and knowledge to tweak settings and overclock (which i wouldn't be doing) ?
1) 4gb - Should be no problem with stability. As for usage, XP/Vista 32 bit WILL utilize upto 4 Gigs of ram, it is just that when 4 gigs are installed only 3.2 +/- 0.4 gigs are available for programs. This has been addressed in several treads, if you would like to read more on this subject.
As far as performace going from CL6 to CL4, There is a boost, going by what I've seen in some of the threads gains are greater for AMD X2 procs than Intel dual's. I think the perforance gain going from CL5 to CL4 is around 3 to 5%. Going from 6 -> 4 would probably be in the neighborhood of 12% +/- 5%
In principle, going from 6-6-6-18 to 4-4-4-12 will increase the speed a fair amount, enopugh to be worth it in my opinion. But the Ballistic ram that you list gets its speed by using a higher voltage, 2.2V, and from what I've read, Dell computers don't allow a person to raise the ram voltage. The result is that the ram ends up running at 667 (PC5300) instead of 800 (PC6400), thus being slower. So in your case, the cheaper and slower ram (cl6) would be your best option because it runs at a standard voltage of 1.8V.