My old machine is 32mb and not worth a toss, so I'm going to buy a 2nd hand unit off the bay to put the truck software on.

Which is the best base model to start with?

Thanks in advance.

The go range is best for me..I have a go520 and a go530 and both work fine.
They are getting difficult to find nowdays.

gezt is spot on.

Look for the cheapest model you can find that has:
1. at least a 4.3" screen
2. at least 64 MB RAM memory
3. at least a 2GB internal memory
4. a SD card slot

Avoid all of these new TomToms released since September 2010. They can't be modified!!
GO 1000
GO 1005
GO 2000
Via Series
GO LIVE 800
GO LIVE 825
GO 7100/GO 7100 TRUCK
GO 7150/GO 7150 TRUCK
GO 9100
GO 9150/GO 9150 TRUCK
Start 20/25/40/45/50/55/60 Series
Blue & Me TomTom 2 LIVE
Sony XNV

Many thanks for the input people! :)