admin wrote:Second internal SATA HD, yes, that's plan B. So, the 2 GB RAM is not optimal but it would work right?
It would. You may have to limit the number of programs running on the host OS (XP) and I'd limit the number of programs running in the guest (Windows 7) to XYplorer.
admin wrote:(Conc. XY mode... the real switch to Win7 will come together with a new PC and LOTs of spare time (unless migrating software can be done automatically in a good way) -- I don't see this coming this year...)
X
P mode, you mean?

I hope the arrangement with an additional HD and VirtualBox works out for you. There is one other option: getting a new PC with 4 GB (XP should be able to use a little over 3 GB of that) and *cloning* the HD of your current PC to a HD in your new PC. There are two challenges with that:
1. different hardware necessitating different drivers (the better disk cloning software like Acronis True Image Home can handle this for you);
2. licensing: XP will require reactivation among possibly others like Adobe software. If your XP came with the computer, it may be an OEM license which dies when changing MB's; otherwise it would be a retail license which you should be able to reactivate.
Assuming you'd outsource the building of the new PC, cloning (whether done yourself or by your dealer) should take no more than an afternoon and would leave you with your current OS, apps and data on much more capable hardware that can eventually be used to run Windows 7 x64. It would be my preferred option.