I purchased a Holux CF Gr-271 gps receiver for my X5 (and now my Ipaq 210).
I used my X5 for road navigation using TomTom (an older version) and geocaching (beeline).
The Gr271 works awesome on the X5 (in my opionion)
Here is the Mfr link.
HOLUX - The Pro Name in GPS
There are other CF receivers I believe that also have slots for an SD card. That migt be soenthng to look at too. try buygpsnow.com.