Thanks, but that info is a bit over my head. What I'm assuming here, and again, thank you everyone for your help (I'll have to come back and give you all good votes on the answers).
What I'm getting is that the 3800+ 2.0G in question HAS to be really 2.4, or else it is actually an 3800+ X2, which the web page doesn't specify.
I take it X2 means "dual core" and as such, an X2 at 2.0 will be more efficient (in general) than the "plain old" 3800+ at 2.4? And either one of these 3800+ will, again, in general. kick the butt of a Pentium P4?
I want to order tomorrow, so unless I'm told otherwise, I'll order the XP system with the Ahtlon 3800+ "2.0", 2X RAM and bigger HD for $15 more than the Vista system.
One other concern which I know is off topic in a way, but may help my buying decision while I'm here, is I was told that Vista (Home Premium in this case) will not run my somewhat dated software, such a Word 2000. Excel 2000 (Office Suite 2000 Business Pro I think), as well as Photoshop 6. I was told I'd be better staying with XP.
Thanks much again.