You may want to rethink that PSU if you are looking to go SLI in the future. That PSU wont work for 2 of the cards that you have without using those power adapters. It only comes with 2 PCI-E power connectors and the GTX 460 SE that you have linked to requires 2 power connectors per card. You can get away with using those molex to PCI-E adapters, but that really isn't the ideal solution. Also, the GTX 460 you listed is recommended to have 24 amps of 12V current. The PSU has 52amps on the 12V rail. That's fine for one card, but with two, you are only leaving yourself 4amps of 12V headroom (24A*2=48A, 52A-48A=4A). If you truley want to go to SLI down the road, I would go up another level in power supplies. A TX750 can be had for $20 more then the TX650. For just one card, that PSU will be fine, but it might not be completely up to the job of running 2 newer cards in SLI.
Also, that GTX 460 will be a decent card, but it will be severely bottlenecked by the rest of the system. I understand the budget approach, but if you could even get your hands on an inexpensive core 2 duo or core 2 quad based platform, you would be able to utilize much more of that graphics card's potential.
Just as an example, my friend at work is currently running a Pentium 4 system with a 9800GT. That card is less powerful then your card, but it still is being slowed down by his CPU. He is forced to play crysis on low settings and only gets 25fps with dips down into the teens on occasion. His GPU should be capable of playing crysis at medium-high settings without issue, but the rest of the system is holding him back. Even if he had a more powerful card, such as your 460, he wouldn't see an improvement in performance because the card is already dis proportionally powerful to the rest of his system.