The way I did it was to make a spreadsheet, and painstakingly include every item of hardware. I'm getting my first mac in 2 months.
Turns out, comparing hardware only, some macs are a better deal, some aren't.
I'm interested in a laptop, so that's what I've been looking at. Specifically, iBooks are a better deal than any similarly priced PC laptop I've found, especially the 12".
On the other hand, though I favor the 15" powerbook, it is nearly identical spec for spec with the hp zt3000 series (when I last compared them, the zt3000 was $1500 and the powerbook is $2000). Same size, same screen resolution, same video chip, io ports, etc. The hp has much better battery life also; my sister in law just bought one, it has a Centrino and it lives more than 5 hours unplugged. Apple only claims 4; some claim to squeeze 4.5 hours out of the powerbook but most people I've seen here claim a bit less than 4 hours as a realistic battery life.
So if price is the only issue, Apple can't claim an across the board advantage, but specific models are in fact a better deal. And though I've only been following the mac scene closely for a few months, I suspect that this changes over time. Perhaps the powerbook will be a better deal when the next rev is out.
As a guideline and starting point, I used this site:
http://www.systemshootouts.org/shootouts/desktop/2004/0831_dt1300.html
Basically, they did the work for you, or at least give you a starting point from which you can work.
Also, there is a "processor equivalency chart" on the same site:
http://www.systemshootouts.org/processors.html
It seems to be a little optimistic on the G4 ratings considering their slower system bus, though I don't have access to a G4 at the moment so I can't be sure. In any case, the iMac has a G5 which uses HT400mhz, and their estimates don't look too unreasonable.
As others have pointed out, there are more considerations than just a direct hardware to hardware comparison. But if apple wins, it makes the whole thing a much easier sell. Just knowing that for certain
some apple computers were a better deal was enough to get
my attention. Now I'm buying my first apple ever. I may even buy the 15" powerbook, in spite of the fact that the HP zt3000 is almost $500 less for very similar hardware. (Given that I won't have the money for another 2 months, I'm hoping Apple comes through with a reasonable upgrade. Otherwise, I may end up with an iBook...)
-kev