Hi Wayne,
Thanks for the warm welcome. You're right, the high end is pretty easy to sort out, it's the lower end with all it's modes, nodes and standing waves that's the hard part!
For the sake of £25/$50 I think it's much easier to go the tried and tested route, so I'll order a RadioShack meter asap, then borrow a friends laptop. TBH I think the speakers I have are too much for the room. I've just spent all afternoon trying the sub in different positions (man that thing is heavy! My back will be complaining tomorrow!) only for it to end up where it was!
Thanks for the input, going to re-read your hard knee post!