Relatively easy to get about. I heard trains were a good way of seeing the countryside. We, however, took buses, which was more to do with sticking to a budget than anything. We were pleasantly surprised, after travelling the length of Thailand in some rickety old buses / minibuses, as soon as we crossed the Malay border, we had 'luxury' (ish) coaches, reclining seats that more or less turned into beds, plenty of legroom, AC, not too crowded either. We booked these from wherever we were staying, or the local travel agencies. In KL, you'll have no trouble whatsoever finding an agent. If memory serves me correctly (it was 2002 when I was there), there are different standards of coach transport you can get, but we found that even a mid-low standard was more than comfortable, and very affordable. I guess anything was preferable to our last bus journey in Thailand which was way over-booked, we were crammed in like sardines, and (worst of all) we were subjected to The Vengaboys album at full volume....twice...not good.
Good luck!