As said earlier, you could upgrade your current system. The only objection that I have about that is the nF3 150 chipset. It's good, but defnitely want the nF3 250/250Gb or newer chipset (depending on socket). If I was going to upgrade your current system, then I would want to swap the mobo and the vid card. If I was going to swap the mobo, then I would seriously consider going the s939 route for future CPU upgrades. It depends on what you want to do and the money that you're willing to spend. It's definitely easier to just push your current system straight to the parents and build your own power machine from scratch. That also gets the parents up and running faster - always good to keep the Mum happy.
Personally, I would hand the current rig to the parents and go the new system route. You have the perfect excuse to build a new system and if you're anything like me, then you're just looking for an excuse anyway.
To save some money I would take that Raptor for your new rig. Format/reload everything onto that Maxtor. That or take both of those HDD and find a good deal on a smaller drive for the parents if they don't need 250GB. Those drives would save you over $300 in the new system - $200 after you factor in the new HDD for your parents.
Make the final decision on if you're going the upgrade or the new rig route and let us know. We'll keep helping with suggestions on components.
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<font color=red>You're a boil on the arse of progress - don't make me squeeze you!</font color=red>