For those who deserted the rolling tie-dyed hills of Berkeley for the funkier shores of San Francisco, or those who have never been East Bay way but want a taste of Visa-carrying idealism, or those acid casualties with a weekend pass from the ward, it's time to join hands and stomp your boots while singing "Give peace a chance," smoking grass, and listening to tales of Winterland long past. In the face of great adversity -- that would be BGP -- the Maritime Hall is celebrating its one-year anniversary with the brother-who-wasn't-as-good-but-survived-the-drug-days-so-now-has-a-musical-career, Gregg Allman. Zero, the Chambers Brothers, J.C. Flyer, and Wavy Gravy open at 9 p.m. on Friday, Oct. 25; call 974-0634. ... Madonna said of the Exotic Erotic Halloween Ball, "It's a fantasy affair, come if you dare!" One has to wonder if she actually visited the "affair," because unless your fantasies include Financial District secretaries dressed as -- ooh, this is a stretch -- naughty nurses and their male counterparts banging their chests while yelling, "You Jane! Me Tarzan!" you're setting yourself up for some disappointment. Fortunately for them, the Exotic Erotic always seems to book the best musical bill in town for the Halloween weekend. This year's lineup includes Love & Rockets and the Tubes. If you can manage to ignore the crowd -- I suggest heavy boozing, the if-you-can't-beat-'em-join-'em gambit -- it'll be great; if you are not the type of person to overlook a lot of rubber penises being waved in your face, save your money for the Cramps (Warfield, Halloween night). The Exotic Erotic starts at 8 p.m. on Saturday, Oct. 26, at the Concourse Exhibition Center; call 567-BALL. ... Due largely to the country's low-key profile, we in America have had very little exposure to the art and culture of Wales. There have been a few notable exceptions, of course: the notorious drunken thespian Richard Burton, the lyrical poet Dylan Thomas, or most recently the film The Englishman Who Went Up a Hill, But Came Down a Mountain. Perhaps even less well-known is the musical tradition of Wales. Next week offers a rare opportunity when the Risca Male Voice Choir, a 58-member group direct from the land of rolling hills and ruddy complexions, makes itself comfortable on the barstools of Dylan's, the city's only Welsh pub. Accompanied by two female soloists, Risca will reveal that the music of Wales is as elegant and poetic as any of its great artists and as haunting and beautiful as the musings of neighboring Ireland. Risca performs at 8 p.m. on Monday, Oct. 28; call 641-1416. This follows a more formal concert at 5 p.m. on Sunday, Oct. 27, at Grace Cathedral; call 776-6611.