Cable GPS receivers wil NOT work with the Mini S so you will need to get a Bluetooth one, still need to get one of these myself so can't personally recommend one (any one else care to recommend one?)
Go with TomTom5 though for SatNav software, you will need to get the 5.2.1 update to make it Win Mobile 5 compatible though.
a 512 MiniSD card should do you as TomTom only uses abput 100Mg, although if you go for a 1Gb or 2Gb card this will give you plenty of storage for MP3's and Videos.
I picked up a 512Mb off ebay for £20 the other day.
As far as setting it up, when you first boot it up it will ask you to align the screen and set the date. Once it has done this it will hang for a few seconds then start instaling the O2 extended rom with loads of Crappy software that slows the phone down really bad!
So when it gives you the option of what type of installation you want (BASIC/CORPORATE/PERSONAL) make sure you choose BASIC. The extended rom will then only install the standard windows build plus O2 connectivity, without all the crappy O2 Active stuff.
Any problems check out the "Wizard" forum (HTC codename for the XDA Mini S/MDA Vario)
Here.
http://forum.xda-developers.com/
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