Well, I know there's a bug in some older 720s that causes ActiveSync to misidentify the 720 as a Pocket PC rather than an H/PC. Try this:
1
) Go to Start -> Control Panel -> Remove Programs and uninstall the Linksys driver.
2
) Download the file
Inflated.zip from the download page you linked above. Open the ZIP file and copy the file
WPC11.H300ARM.CAB onto a CF card.
3
) Place the CF card in the 720 and run the CAB file on the 720.
Let us know if this works.