The item that you referenced is correct for your M3.
MY08 M3's utilize a DVD based navigation system. MY09 and newer M3's utilize a hard disk based navigation system. So, to update an '08, you simply buy a new DVD. Updating '09's and newer requires a trip to the dealer. Both methods have their pros and cons.
A few more thoughts. Used (and occasionally, new) BMW navigation DVD's are readily available on eBay. You just need to ensure that what you're buying is an original OEM DVD, not some copy that was burned by the seller. Look for the hologram around the center opening. Also, navigation updates are primarily focused upon merchant updates (restaurants, hotels, gas stations, etc) rather than upon updates to actual roads. If you don't travel very much or live in an area that is confusing to navigate, the expense to update your system may not be necessary.
I hope this info helps!
New: /// E92 M3 /// Interlagos / Novillo / Carbon /// DCT /// Tech Pkg /// Prem Pkg /// Premium Sound /// 19” Wheels /// Heated Seats /// iPod / USB /// PDC /// Sat Radio
Mods: /// Modular Concept 01’s /// Meisterschaft Exhaust / Aero Shield / Carbon Tips /// Smoked Tails /// Matte Black Grills ///