The decision of choosing between those processor speeds are akin to the question of which car you buy. Sorta. The faster it is, the better things run. Actually, that car bit was an outright lie. Just a side note, if you're playing higher-end games such as BF2, CoD2, ET:QW, and so on, then 1.66 may not deliver that well. I've got a dual core 1.60 with 2 GB of RAM, and it's barely running my games on Low/Medium-Low. Then again, it is a laptop with sucky integrated graphics, but 1.6 GHz dual core on a desktop would still let you "just get by".
Although I do understand your position, since I'm trying to build a gaming machine on part time wages, try to find some good deals and treat yourself to
at least the 1.83. You'll be glad you did.
http://www.tigerdirect.com
http://www.newegg.com [Recommended]
http://www.ebay.com [Not-So-Recommended, But Still An Option]
Last but not least, the RAM is more than sufficient for what you'll be doing, and the video card sounds like it's good. Kudos in those departments. BTW, what's the video card model? If you need assistance, I might just help you out with buying your processor, really got nothing else but robotics to spend my money on!