Dude, I did recommend a power supply, check the last link in my last post.
A 4850! Good call by patonb, they're great. If I recall correctly, when the 9800GTX+ came out, they were neck in neck with the 4850, it just came down to preferance. Oh and by the way OP, a GTS 250 is just a rebranded 9800GTX+. Which is stessentially a 9800GTX haha. Really comes down to which ever is cheapest at the time, 4850 or gts 250.
Oh dude, a GTX 260 over the GTS 250 without any question. But that one you posted is a refurbished one. I can't really comment on it, haven't ever purchased a refurb video card.
I haven't ever used a Rosewill PSU, I stay away from them. I've heard little, but they aren't a choice PSU brand.
EDIT- If you do want a gtx 260, or just a bigger PSU, like a 550W, I would highly recommend this-
Newegg.com - Antec BP550 Plus 550W Continuous Power ATX12V V2.2 SLI Ready CrossFire Ready Modular Active PFC Power Supply - Power Supplies
Really good PSU, I've used it in multiple builds for others.