Private transport
Car / Motorcycle
As it has been said on the "Getting there" page, the road network is well developped here, so there's no problem to travel all around the country using a car. Another good thing you might want to know is that you can cross the country from east to west in approximatively 3 hours (300 km), which offers that advantage to see a lot in a short period of time.
You want to rent a car ? .... you'll find informations you need about it in the "Sharing a ride" page.
Bike
In Belgium, we encourage people to move by bicycle, especially in Brussels and in Flanders. More and more facilities (park places, cycle paths) are there developed.
For Brussels, the website "Cycling in Brussels" gives you a lot of informations and practice advices for your travels by bicycle... Useful, even if you're not living in Brussels!
In Flanders, you'll find the most important network of cycle paths, maybe because of the relief, not really hilly! You'll find many informations and advices on the website of the mobility in Flanders: "Mobiel Vlaanderen" [NL]
In Wallonia, cyclotourism is above all developed, with the "RAVeL" [FR]. It's a network of paths and itineraries for cyclists, pedestrians, roller-skaters, riders, etc.
Rent a Bike
If you want you can just hire a bike in several train station in Belgium. The list of the stations that offers this service and prices informations are available here.
Otherwise, you can rent a bike in some other town but you have to check with the local tourist information point.