There are at least bands with this name:

1) Czech Beltaine's music is based on a combination of doom and death metal with pagan elements and touches of folklore. Their music doesn't also deny the roots in the classical metal and rock feeling. That's all covered in a modern sound with deep charismatic vocal and growling on the top of it. They formed in 1996, and released one record so far - the highly acclaimed "Bohemian Winter" in 2003. Their lyrics are about Bohemian mythology, paganism and are nature-inspired. Their official web : http://www.beltaine.net

2) Beltaine Celtic Group is one of the new Polish bands playing celtic folk.

Polish Beltaine group consist of five young men playing traditional Irish, Breton or even Jewish music as well as their own songs.

Polish Beltaine relased one record so far - called "Rockhill" and it was very warmly welcomed along the folk-fans in Poland. They are playing with "power and energy" and they have very special and interesting contact with audience during their concerts - that makes them "a lifetime experience".

3) There is also another polish band called Beltaine. They are from Warsaw and play climatic rock/folk similar to Dead Can Dance or Deep Forest. Members of the band:

Sebastian Madejski - vocals
Paweł Drygiel - guitar (and other instruments)
Michał Pietrusiewicz - bass guitar (and other instruments)
Daniel Paulinek - synthesisers, drums, vocals

4) Another folk project, headed by Omnia's Jenny. They had only one CD release, 'Celtic Harp' in 2001, which is sold out. Currently there are no plans for a rerelease or to continue this project. The music this project makes is centered around harp music, playing mostly traditional songs.