Sure you can install the OEM MFD Navi. I recently did this...
You need to decide whether you want the D or G version of the MFD. The D and G version MFDs talk to the steering wheel controls and full FIS cluster display differently. You choice will depend upon where your car 1) has steering controls, 2) full FIS cluster, 3) CAN-BUS or 3LB support for 1&2. You might also need a TMC box, if you decide to go with the G version.
Additionally, you'll need need the appropriate harness for connecting the MFD to the OEM radio harness (and a few other connection behind the cluster.) This choice depends upon whether you have a 1 DIN or 2 DIN OEM radio.
Of course, you'll also need a GPS antenna, and a set of map discs. Steve Z1 sells complete packages of all these items for reasonable prices. Search for him.
If you post answers to the following questions, I'm sure we can help you decide what you need:
0) Exactly have year, and model B5 do you have?
1) What OEM radio do you have?
2) What kind of connections are on the back of it?
3) Do you have steering wheel radio controls?
4) If so, do you have multifunction relay 451 or 452?
5) Do you have a full-FIS cluster?
6) If so, does it use CAN-BUS or 3LB? (Use VAG-COM to get it's part number.)
7) Am I missing anything...?
I was wondering if its possible to put Vw OEM navigation in a B5.
If it is possible, what all do you need, how tough is it to hook up.
any in put would be great.