There are (were) 3 Indians in Longford town. Theres one above a pub near the train station and that's quite nice. Another is on a street going from Longford towards Dublin - sort of on the street facing Super Valu. I've a feeling that ones closed down though.
The third is upstairs in retail park that has Aldi and it's absolutely disgusting. I tried it once and couldn't go back. It looks great and the staff are very attentive but the food is really bad.
The Aubergine Gallery in Longford Town (Above the White House pub) is pretty good ... they don't take bookings though. Alternatively you could try the Black Olive across the road (on Ballymahon Street). There is an Indian restaurant in the Aldi Shopping centre ... can't remember the name though ... or if you like chinese, the chinese gourmet on Dublin Street is pretty good too.