I got the replacement motherboard and Turion 64 x2 Ultra CPU in the mail over the past two days to rebuild the Toshiba Satellite that I found and it's now on my bench loosely assembled and it works! I have enough of the screws to make it solid again, but many of them were missing when I got it. (It's not as if we don't all have thousands of loose screws and fasteners in bags and boxes somewhere, right?) It looks as if the motherboard may have been replaced once before because there was a plastic connector that was taped together but I managed to work out a solution to make it work and that connection should be more solid now than it was.

Original specs were

AMD Sempron SI-42 2.1ghz
250gb hard drive
2gb RAM
AMD Radeon 3100 graphics (underclocked 3200 that seems to be unique to Toshiba from what info I can find)

The replacement CPU is a Turion x2 Ultra ZM-85 2.3ghz dual core

Windows Experience scores before (I didn't actually run these since the original motherboard didn't boot so I used the scores the previous owner had saved)

Processor 4.1
Memory 5.2
Graphics 3.1
Gaming graphics 4.5
Primary hard disk 5.4

and after

Processor 4.9 (19.5% improvement)
Memory 5.2
Graphics 3.4 (9.7% improvement still stock clocks, haven't downloaded RivaTuner to bump the clocks up yet)
Gaming graphics 4.8 (6.7% improvement)
Primary hard disk 5.4

Still pretty low end but a lot more bearable than my Acer 1.6ghz Athlon Neo laptop (I actually have a Turion64 x2 for that one around here somewhere, too. I think I'm feeling brave enough now to upgrade that one after getting this one to work)

Memory and hard drive ratings stayed the same since I didn't make any changes to those systems, but a faster hdd and more memory are already in the works. I credit the graphical improvements to the stronger CPU since I made no changes to the video, either.

For anyone else wanting to attempt this, I recommend staying clear of the two fastest speeds for any generation of Turion x2 as the prices for those are ridiculous. I got the CPU for this one for like $17 and the one for the Acer for $12 by going two tiers down from the top. The faster ones still trade for $40-$50, which would have killed my budget for this upgrade. You also have to be careful that you know which generation socket your laptop has and which CPU's will work in it. Different generations of socket S1 are mechanically the same but not electrically compatible. My Acer is S1G1 while the Toshiba is S1G2.