"2 Meg" is meaningless unless they also tell you which parameter is needed. A 2 meg(a pixel) image will be a lot different to a 2 meg(a byte) file. My guess would be that they want a relatively small file to work with, so they probably want a 2 MegaByte (often expressed as MB) file.
Your D90 will give you 4,288 × 2,848 (12.3 effective megapixels) but I'm not sure what size files it will give you straight out of the camera - my guess would be 4-8 MB files (based on my old D200's large fine JPEG file sizes). A 4 MB file straight out of the camera can be saved (using Photoshop Elements) at quality 10 on the slider (which still gives plenty of quality) giving a file of 1.6 MB - well under your club's requirement! If my maths is any good, that's 40% of the original file size, so if you have an original file of 10 MB, it'll shrink to around 4 MB using the same setting and further quality reduction will reduce the file size even further. If you also resize the actual image (in terms of Mega Pixels [or MP]), it shouldn't be difficult to get a file that's big enough to judge (in terms of MP) but small enough to transfer easily (in terms of MB).
Now to explain MB, KB etc... The first letter denotes the multiplying factor - M = Mega = 1,000,000 while K = Kilo = 1,000 (the actual numbers are slightly different when talking about Bytes [the "B"] but it's close enough for government work!) and the case is important - M - Mega but m = milli... The second letter denotes the units B = Bytes and is a measure of file size while P (in this context) = Pixels, which are Pi(x)cture Elements - not usually visible to the naked eye but if you zoom right into an image at 400% in an editing programme, you'll see them as individual squares of colour.
Not sure if Realspeed's recommended software downloads to Macs and it's not a package I've used. There are many options as far as software goes ranging from free to rather expensive. I would use whatever you know best.
