OSNews

Dell Dimension 4600:
P4 3Ghz
Windows XP Pro
3 Year Warranty (There are a lot of plans of Warranty & Support in their web, I think that you have to buy telephone support separately)
512Mb DDR PC3200
160Gb Serial ATA
Floppy (You need it to install Windows XP... :/ )
8x DVD+RW
RecordNow! MyDVD Deluxe
Intel Extreme Graphics 2
Sound Blaster Live! 24bit ADVANCED HD
Firewire Adapter
Ethernet 10/100
1,327$

Lacks gigabit ethernet, firewire 800, a good graphic card (wich isn't a build to order option), software, quality, 64bitness.. etc etc..

Dell Dimension 8400
P4 3,20Ghz
Windows XP Pro
3 Year Warranty (There are a lot of plans of Warranty & Support in their web, I think that you have to buy telephone support separately)
512Mb DDR PC3200
160Gb Serial ATA
Floppy (You need it to install Windows XP... :/ )
8x DVD+RW
RecordNow! MyDVD Deluxe
128Mb ATI Radeon x300
Integrated 5.1 Channel Audio
Firewire Adapter
Gigabit Ethernet
1,496$

I don't think these parts are as standard as you say because i have to add it to the base configuration..
Also, for de Dimension 4600 there isn't an option for other graphic card than Intel Extreme Graphics 2..

If you start adding the things that a mac gives, it isn't cheaper, sorry for you..

And, no, AMD 64Bits cpus doesn't blow G5 cpus..

http://www.barefeats.com/pentium4.html

Actually, the two CPU are similar in performance..

Don't forget that IBM is the company that makes both processors in their fabrics.. The same for Nvidia GPUs and others..