I think I found the auction you are talking about, and I would go with the iBook if I had to choose between only those two options. From the specs that I am looking at in this auction, it looks like they are the same, but the video card in the new iBook is better. Additionally, it is new computer with the Apple warrenty. Now for my personal choice, which is neither of the two computers (!)....I would either save a bit and get the 12" iBook or spend the same amount and get the 12" PB. I really would not get the used 15".
I recently purchased a 12" iBook with Bluetooth and a 60 GB HD. I also bought 3rd party RAM for a total of 640 MB. The computer is plenty fast and zippy for what I do, and I am very happy. Since I do not do any video editing (I do not have a video camera or the time currently), I did not need the SuperDrive or all the extra goodies that a new PB has. Besides, I plan on getting a desktop for all that.
Here are the specs from the auction I was looking at so you can compare them to your auction:
867MHz PowerPC G4 (iBook 933 wins)
1MB L3 & 256K L2 cache (this I am not too sure about but I know the iBook has 256k L2)
133MHz system bus (iBook has the same)
512MB SDRAM memory (iBook wins because it has DDR and you were going to upgrade it to 640MB)
40GB Ultra ATA drive (the iBook wins with 60 GB)
Combo Drive (DVD-ROM/CD-RW) (same)
ATI Mobility Radeon 9000 w/32MB DDR video memory (iBook has the ATI Radeon 9200)
Gigabit Ethernet (same)
56K internal modem (same)
1 FireWire & 2 USB Ports (same)
AirPort Ready (same, but I think the iBook has the new and better antenna, I could be wrong)
OS 10.2 (iBook wins, you get Panther 10.3)
Also, the iBook sports a 1 year warrenty and you can get it BTO with Bluetooth. Of course, you could buy an external Bluetooth adaptor for the same amount for the both at a later date.