well normally I texture on a bitmap of 1024x1024 which usually takes up around 5mb, plus 35mb within photo/paintshop
but thats just for creating, adding painstating detail - then its all shrunk to oftenly 256x256 and almost all that detail goes

but its a point to note, should work on larger maps and then scale down to your needs ... and they tend to gain some nice neatness around the edges as it blends pixels when you shrink.
remember it isn't the UVmapper which changes the size of them but the actual detail you decide to do. Whenever possible try to put the areas of the model which need to look identical to each other overlapping, this saves considerable space
Anata aru kowagaru no watashi! 