Thank you both for the advice, much appreciated
cordis - I'd forgotten about velcro, might give that a try.
The motherboard has integrated graphics and I intend to use those.
JamieG - specs are
Samsung F1 1TB HD
Asus M3A78 motherboard
AMD Opteron 8450 2.1GHz (triple core)
120mm fan at the front
Seasonic 430W PSU
The fan grill pictured in the original photos was only a 60mm unless you saw a review? - see below.
Good idea about sealing the rear 2 x 80mm fans grills, might try that.
The HD cage is removable but I'd rather put the HD in front of the 120mm fan in the lower section, not sure how I'll put it there but...
Should I cut out all the grill in the photo below or just the outlined bit for the PSU?
Should I cut out the lower fan grill (120mm)?
I've already sealed off the 3.5 FD slot