The Sony Ericson site only has the themes creator for windows. Is it even possible to make them on my mac?

Thanks in advance,
-mocabre

No - unfortunatly no software available yet on the mac. I produce all the graphics on my mac and then just compile them on my pc. You could do the same if you know someone with a PC who is happy to let you do it.

If you know how to write the xml code for the theme you want to make and know all the sizes you could in theory do it manually, however you wont be able to see any previews

All you'd have to do is put all the files, images and the XML file, in a tar archive and rename it *.thm (i think that would work?)

Here's a SE Theme Creator for MAC:

http://myforum.<url snipped>.net/attachment.php?attachmentid=2228

Hope this helps