I'm not sure the 5200 would do any better graphics wise, the 690G has basically X700 SE graphics. The 5200 has 2 pixel pipelines, and the 690G's X1250 has 4 pixel pipelines. You already have PCIe x16 on your board, so why bother with a PCI card?
The Geforce 5200 is the absolute worst Nvidia card ever made. It's junk. If someone offers you one for free, don't even bother. If you must have Nvidia, find a $50 card of more recent vintage, but AVIVO is better than Pure Cinema on the cheaper cards, so I'd go 3450 instead.
Yeah neither will be worthwhile for games. Run the dedicated video card.
Before we got a card for my wife's 690G build, she could still run Morrowind with shaders enabled at 1024 x 768. I doubt the 5200 could manage that. Seriously, getting the RAM back by using a card like that? What kind of advice is that from you guys? RAM is cheap. He could add more if he didn't want to get a new card.
A PCI 5200, or it's ATI low end competition from that generation (the 9200) just is not worth it nowadays, not compared to integrated graphics as good as that on the 690G and V boards, or the Nvidia 6100 and 6150 boards either.
For that matter, he could transfer his CPU to one of the new 780G boards and then get a 3450 for hybrid Crossfire, or he could wait for the new Nvidia DX10 8200 boards in April and get hybrid SLI with a $50 Nvidia card of recent vintage. All sorts of things he could do that's better than replacing what is essentially an X700 SE with a 5200.