Good luck! It now includes a FREE service and premium for $2.99
Just tried it and the basic service and it's really fast, i might prefer it to google nav
EDIT: Added apk, hope it helps!
EDIT 2: Found this on Captivate Apps Section, so please don't think I am taking any credit.
Apparently: "if you go to the Telenav OTA site at ota.telenav.com/tn and click T-Mobile as your carrier, then click the Vibrant 4G, it is completely compatible"
"Also, unlike Google Nav, TeleNav will continue to work without a tower signal, it will just tell you to turn without the street name"
Good luck. I have a myTouch 4G running CM7 nightlies and was able to find it on market and it works so good luck!