Should I buy this new Dell PC and monitor combo for $800?

That PC lists Win7 64-bit, so you just need to check the compatibility requirements of the software you’re intending to use to make sure that’s ok…The 20″ monitor is a little small, and the 2Gb RAM is a little lean, but it’s usable; you can probably upgrade later if/when needed.

I’ve sold ~30 of a small-form-factor HP with multi-core CPU, 4Gb RAM, SSD HD and W7 Pro x64 and dual-monitor capable for ~$859 and people LOVE them – they feel really really fast. For business use I highly recommend 4:3 (1280×1024) 19″ (not widescreen) dual monitors – that way you’ve got your email up on one and your business app up on the other, so you aren’t flipping back-and-forth all day every day for the next few years.

Here’s a recent quote I sent to a client, just to give you an idea. If you wanted to add dual monitors, they’re ~$180 each (x2) plus tax.
859.95 HP Business Desktop, SFF, multi-core, 4Gb, Win7 Pro, SSD HD
259.95 Microsoft Office 2010 Home & Business
29.95 DVI to HDMI cable for monitor #2
18.61 Shipping (FedEx Ground)
1,168.46 Subtotal
96.40 Sales tax
$1,264.86 Total
HP Business Desktop, SFF, multi-core, 4Gb, Win7 Pro, SSD HD 1 859.95 859.95

Sure this strategy costs ~$600 more than the ~$900-1,000 Dell package (after 4Gb RAM and tax), but if you look at your total cost of ownership over the next 3-5yrs vs. the increased productivity over that time period, it’s well worth it. If you can swing it, you’ll be glad you did.
I’m happy to help you in any way I can.