Just to help you, here are the different switch types (that the zaptel driver can handle):
national: National ISDN 2 (default)
dms100: Nortel DMS100
4ess: AT&T 4ESS
5ess: Lucent 5ESS
euroisdn: EuroISDN
ni1: Old National ISDN 1
qsig: Q.SIG
I've already done 2 Vicidial/Asterisk installation using ISDN PRI trunks and had no problems. Used 2 different cards: Digium TE120P and Digium TE220.
A word of advice: make sure that the ISDN type selector jumper is set to the correct one (T1 or E1). Spent half a day tearing my hear out during the first installation coz the card didn't want to communicate with the telco's equipment...