It looks like Real Player only installs from a cab file on the X51v. There are instructions on their forum for getting the cab file and installing from it
here.
"start installing
when you get the error message about your activesync version leave it , do not press ok
the setup has temporaryly put the install files in a temp file
if you press ok in the error message the files will dissapear
so leave it
when usin XP go to "c:\Documents and Settings\Windows username\Local Settings\Temp\~rnsetup\"
when using win98 go to "c:\windows\temp\~rnsetup\"
copy the "realplayer.cab" file
copy this to your pocketpc
you can open this file and it will install (but the cab will delete itself after install)
or open it with CabInstl a install utility for pocketpc's (google it if you do not have it, great prog. if you have cabs for your software you do not need activesync to install)"
An easier method to get the cab is to use WinRAR to extract the files from the msi or a freeware msi extraction utility like
Less MSIerables. Get the cab, copy to device, and launch using file explorer on the Axim.