I am pretty sure you can't do that. I did a quick search on google with no result, and I have never heard of anyone doing it before.What I suggest is you clear as much out of your RAM as you can (ie. install all progs on a CF)
For the wireless, look for cards that has drivers for Pocket PC 2000 for MIPS processors. It can be either a Type I or Type II card (type ii is thicker) as the Casio has a type ii slot compatible with both i and ii).
This one seems to do it (
http://www.expansys.com.hk/product.asp?code=DCF-660W ) look for it at your local shops or online.