What the TH2G does is trick your GPU into thinking there is a ultrawidescreen monitor connected and then splits the signal to 3 monitors. You can then use the Matrox software to devide the very wide desktop into 3 virtual screens (remember windows still thinks it's a widescreen).
That's the thing that's going to make the video a little tricky, but easier than some implementations. You won't be able to widescreen the video onto separate monitors, and instead there will be 2 video windows open in conjunction with the main desktop. Alittle nightmarish on the workload, but as long as they don't require acceleration or VPU assistance it should be ok, and no need to worry about overlays.
Your GPU is already pushing it's limits rendering a 3840x1024 desktop.
Without video acceleration it should be ok for 2D.
My advice stands, if you want 3+ screens then you should get yourself a Parhelia. Get a PCI or PCI-X version that will fit into spare PCI slot.
Too bad there's no P750 in PCIe form, save a few bucks. He would also be able to get away with an R9200SE PCI add-in card in addition to what he's currently got. And for any non-Matrox solution (and even Matrox if you have extra coin) I would recommend getting a dedicated 3rd party multi-monitor program like UltraMon which really gives nice added functionality and ease of use compared to Hydravision and nView.
Just want to add that if you are running things on DVI or high-res monitors then you might want to consider a Matrox QID (quad monitor support) that can handle 4x displays running at 16x12 DVI. The QID also comes in AGP, PCI, PCI-X and PCIe flavours.
Just a little pricey though, but definitely a good choice for 4 monitor there's also the ATi FireMV and there's even a GF6200 based quad monitor card out there, but it's hard to find.
As for SLI/Crossfire, you can software disable via windows and connect your monitors to 3 free VGAs.
But don't use the SLi or Crossfire, it just mucks things up for the most part. But 2 PCIe cards (2 X300 or 2 GF6200) would be fine, but that requires a new MoBo, and likely with Dell other new parts.