As for the dual monitor question, it doesn't put any strain on your system whatsoever. Any $20 graphics card with two plugs could run them as good as the latest and greatest cards.
I have three GPU's.
Two NVidia 7900 GTX's and a GeCube Radeon7000 ($29, 2 yrs ago). NVidia fucked up and made these two cards unable to run dual monitors while SLI was enabled. They fixed it with an updated 7900GTX a few months later but it was too late for me as I bought them when they were first released. I bought that cheap Radeon7000 for the second monitor.
If you've ever considered two monitors, I highly recommend it. But be forewarned, you'll never be able to go back to just one.