Hi pdurrant and thanks for the advice. I saw Mobipocket mentioned quite a lot on here so I did download and install it on my Omnia last night. I also downloaded their conversion tool but have to plead ignorance as to where in my Omnia's file structure I should put the converted file! I've only had the Omnia for a week and am still working my way around all it's features.
I don't read eBooks on my PC so unless the stand alone conversion tool really doesn't work I'm not sure I'll need the reader for Windows. But I'll bear it in mind if the stand alone doesn't work.