PSU for new rig

[OneWingedAngel]

Can any one reccomend a good and preferably cheap psu for use on the following system?

Pentium D 920
Abit lg-81 motherboard
2GB PQI turbo DDR-2 667 memory
x1900xtx 512mb graphics card
160GB Sata2 maxtor hard-drive
nec dvd-drive

all mounted into an aspire x-qpack. The. size of the PSU is important as not all seem to fit (especially with nec drives) I know the enermax liberty would fit but would the 500w model be strong enough or would I need to go for a higher rated model?

Thanks

 

[OneWingedAngel]

Would the 500w liberty have enough in it to overclock a lot? I'm hoping to get the cpu to around 4ghz.

 

[OneWingedAngel]

From many reviews i've read it's not struggled with an SLi rig with both oc'd CPU & GPU's. and that's just the 500W version. Many people underestimate the power of PSU's, and go for 700W + when to be fair it isn't needed.

that was my worry, either going oerkill and getting a 620w version for over the odds, or buying an underpowered one and having to get another one.