Hey RedUK, I got my machine up and working and my PSU seems fine. I haven't really noticed the PSU fan not coming on, but I've just seen is now, and well like PZ said, it won't come on until it needs to. My CPU is at 33 when idle, my GPU is at 36.5 idle and my case is just under 30 when idle.
The crazy thing is when my GPU is under full load, it heats up immensely and I start to worry. ButI hear that is normal.
Your PSU is fine.
<center>Athlon 64 X2 Dual Core 4200+ 512KB l Gigabyte GA-K8N-XP Sli Motherboard l XFX GeForce 7800 GTX 256Mb (450/1250) l OCZ 2Gb (2 x 1Gb) Dual Channel Platinum Series DDR400 l Maxtor Diamondmax 250Gb SATA 7200rpm 16Mb Cache l Enermax 600W Noisetaker l NEC ND-3540A Black Dual Layer DVD+/-RW l Sony 3.5\" FDD l Black Coolermaster Aerogate 2 Fan Controller l Extreme Gaming Spider Case l Viewsonic VX924 19\" TFT 4ms Response Time l Logitek MX518 l Saitek Eclipse l Windows XP Professional Service Pack 2</center>