Given that Market usually updates itself... you should have the recent version installed.
However, if you don't have Market 3.4.4 installed and you actually want this version...
Make sure your phone is rooted!
Get yourself a copy of Market 3.4.4.
For example, download
eagleeyetom's Android Market update for CWM and pull the Vending.apk out of the update ZIP.
EDIT: Errr... better use the link in my signature and look into the "Android Market" folder - eagleeyetom has not updated the links in his thread yet. *goes shooting him a PM*
Copy Vending.apk onto your SD card (i.e. into the root of the SD).
By using Root Explorer or Root Browser do the following:
RENAME /system/app/Vending.apk to Vending.backup
Move /system/app/Vending.backup to /sdcard (just for safety in case we need it again)
Copy Vending.apk from /sdcard into /system/app
(Don't forget to tap "Mount R/W" first in Root Explorer)
Adjust the file permissions to
R W -
R - -
R - -
Reboot your phone!
Once the phone has booted up again open up Market ... if it works you now got the latest version.
If it doesn't work just reverse the procedure and restore the Vending.backup as Vending.apk in /system/app and reboot afterwards.
On a second note - if your phone is rooted and you have xRecovery installed ... in eagleeyetom's thread there's also a dual-recovery update ZIP you can flash through xRecovery - look at the last few posts in his thread.