Ciampino is a 'one man and his dog' type of airport, which I'm rather fond of. When i was there, a few months back, there were no delays when checking in. It only took me a couple of minutes to get through the security checks. However, as Lil O'Lady suggests, the facilities can be rather stretched if there are several flights around the same time. (Be prepared to queue for the loo).
If you're travelling with others, it might be worth considering a taxi. They're strictly regulated by the local authorities, with a fixed fare of �30 to, or from, any point within the city walls.
There are two bus companies operating direct services to the city centre. Terravision (which Ryan will encourage you to use, because they've got a partnership) will take you to the Via Marsala, immediately outside Termini rail station.
SitBus also operate to the Via Marsala, but they use a different stop which is just along the road from Termini station. SitBus is marginally cheaper and also operates later in the day than Terravision do.
http://www.adr.it/portal/portal/adr/Ciampino/S ervizi/Come_raggiungerci/Arrivo_bus
You can also take a shuttle bus, for just �1, to Ciampino station, and then take a train into Termini station.
To get around the city, you should either use BIG or BTI tickets. A 'BIG' (
biglietto integrato giornaliero) costs just �4 and gives you a day's unlimited travel on the buses and the two metro services (as well as some local rail services). The 3-day version is the 'BTI' (
biglietto turistico integrato). The tickets are available from machines at metro stations but they only offer limited change. (If your transaction would require the provision of more than a few euros in change, it's rejected. You get your money back but no tickets). It's eas