The situation :
Video card died, laptop wouldn't boot up, and there was some kind of error message about memory.
This has been a slow-moving process, as it needed me to have time (around work, fencing, and Bub), and energy (hi Bub!) to look at it, and motivation was sometimes a bit short too (I have some games on my mac, enough to keep me occupied :) ).
First thought was RAM, and I wanted to upgrade from 2Gb to 4Gb anyway, but that didn't improve anything.
Second thought was video card - and here I was lucky, in having a laptop using a MXM-compatible graphics card. I think the original intent was for laptops which could be upgraded just like desktops, although in practice the four (or more) different MXM standards, and limitations on power/cooling inside a laptop, probably made this uncommon. However, it did mean that I could get a compatible replacement card off eBay :)
Delicate surgery was performed, the card was installed ... and neither XP or Linux would start.
However, a USB drive with a later version of Ubuntu started up fine, giving me some hope that just a little software maintenance would be required.
First, there was an annoying error message at boot, which came with 30+ seconds of loud internal-speaker beeping and waiting and an announcement that performance was being throttled. (And if I ever find the engineer who thought that was an acceptable way to deal with an issue, there may be a different kind of throttling going on :-) )
Anyway, eventually I came across ways to reflash the graphics card's BIOS, with modifications made in a binary editor to resolve the beeping/waiting (well, beep disabled, delay changed to 1 second, annoying message still present).
At this point, XP was still hanging while booting, and it was time to delve into trying to repair it. First plan was to use the install disk and try a "repair" install, but it didn't offer me that option. Second was to tinker in the recovery console, but that was blocked by an administrator password being required and not being bypassable.
Finally found some combination of copying files saved as part of system recovery (e.g. registry files) and/or deleting/moving some driver files that appeared to be causing the hanging (all of this done booted into the Ubuntu USB drive mentioned earlier), and got the machine to boot.
Yay ! But ... the system was fine in normal use, but very slow in anything requiring 3D (around 2600 in 3DMark06, compared to 8000+ originally).
"Oh, this'll be due to the throttling", I realised (eventually), and set about doing something about it.
This needed more tinkering, more BIOS editing, and numerous reflashes of the graphics card BIOS again to find settings that were acceptable, but didn't cause system crashes/blue-screens at regular intervals.
Finally, I've reached a point where it seems almost stable - it does randomly restart every now and then, I suspect I need to lower the graphics card settings slightly again. However, 3DMark score is back up to 7600, and ... I can play Skyrim again :)
 Notably, Civ2 and SMACX - and that's why I'm holding off on upgrading from Snow Leopard just yet, because the compatibility/emulation/whatever that let me play them are gone in Mavericks.
 This laptop is 6 years old,
Original post on Dreamwidth - there are comments there.