
Interesting you should ask because I've thought of going there myself. I was working in the Czech Republic about 5 years ago, up in the north near the Polish border. I had a truck and used to take off when I had free time - the Tatra mountains there are full of unpaved tracks, and the roads are (or were) deserted - a legacy of communist economic mismanagement that I've seen in a bunch of other countries.
You should email this chap -
tskrzypiec@pgnig.com.pl
He lives just over the border in Poland, speaks/writes perfect english and is a very keen MTBer - lots of useful info.