If you have a big monitor, not much. But with a smaller monitor/lower res settings, you'd be able to play whatever you felt. It really depends on how much you game, what games you play, and how high of settings you want to have on your games.
However, it looks like you're trying to make a system on a budget, so you may want to go for one of the high end 6000 series cards and spend a lot less than 300 bucks and get a good card to boot. The 6600 (regular, not GT ) outperforms the 7300 in many benchmarks, and in many others they are neck and neck. A 6800 would certainly outperform both in any game you can get today, and would likely cost ~150. Ebay is your friend in this case, as I learned when buying 2 6600's ($50 ).
I don't recommend getting anything LE from nvidia, as they often signify Lowest-End (my term :wink: ) and are easily outpaced by midrange cards of the previous generation, even those with half the RAM.
For the rest of the system, its pretty ok for a low end system, although you may want to bump it to 2 gigs for a future vista purchase (memory hog!) and if you can afford it DDR2 800, although the 667 should perform pretty well anyway.
To sum up: No serious bottleneck, Don't get an LE, and more RAM is your friend on the motherboard. The processor will overclock quite well (so I'm told) and with a previous generation, high end card, so will the GPU. Higher speed ram definitely helps with that as well, but you can overclock ram just like you can anything else.
The 7300LE will do little for modern games; however, don't pay Dell $200 to upgrade to a 7600gs. Buy an aftermarket 7900gt or x1950xt card instead- they have been seen for under $200 and will be faster than the gs.
I was referring to the 7300 and 6600, sorry. The 7900 would be hella expensive in comparison to the rest of the system, so I was kinda ignoring it. If you wished to spend the money, the 7900 would pwnzor all three, but at a much higher $$$ than any one of them, maybe even all three put together!
The President is right (unless he is G.W.Bush) , it all depends on your Monitor and your gaming needs, if u have a 21" monitor or above, then u will get extremely poor fps, but if u have a 19" or less one, then i suggest waiting for the new 8600 to come around (probably in a month or so) they will be perfect for u and u won't have to upgrade again for a DX10 card.