|"i want to upgrade the psu for a better one (maybe 700w or 600w)"|
The PSU should defintely be upgraded but you certainly don't need a 600-700W unit. Try to keep your "investment" as low as possible, it's not worth sinking too much into an older system (AM2, DDR2, 6150SE/nForce 430). You can get this Corsair 500W for just $30 (after promo code & rebate) but you must buy today:
Or there's the forum favorite, the Corsair 430W for $26 after rebate:
"buy a new graphics card ( visiontek radeon 5670, GTX 460 or one similar to it)"
There's a world of difference between the two. The HD 5670 is an entry level gaming card plus it's an older model so it's getting hard to find. The GTX 460 is a much higher end card but it requires almost 3 times as much power (61W vs 160W). See the comparisons:
"maybe later on upping the processor to a AMD athlon IIx2 270"
Look again at the motherboard link your provided - Supports AMD® AM2 Socket K8 Athlon™ 64 X2, Athlon™ 64, Athlon™ FX, and Sempron™ processors under 89 watt power consumption.