Seriously, unless you intend to reuse the MB/powersupply, the whole 'Dell doesn't use off the shelf parts' is a non-issue for 99% of enthusiast owners. You can replace the CPU, GPU, Memory, HD, and any other card you may want to. The only thing proprietary to Dell is those two bits.
Edit: I also run Win7 64, and I rarely have any problems - only with truly ancient stuff.
Edit: I also run Win7 64, and I rarely have any problems - only with truly ancient stuff.