ok erm it has to be 100x100 apparently
so fix a squere i guess
make that the size with ctrl+als+i
OR
uplaod you pic on a thing like photobucket
and try to uplaod it on this site with the direct link

ctrl+alt+i
thats size thingy

just make a picture the recomended size in photoshop or paint or whatever
save as..
.png

uplaod
done

Photoshop
save as png
[=
hope that helps
xx