Strange things happen on Buffy the Vampire Slayer and Angel all the time, but none stranger than this. Buffy's Alyson Hannigan, who plays the Chosen One's sorceress sidekick Willow, will be appearing on the spinoff series in the March 26 episode of Angel. Since the supernatural shows are now on different networks — Buffy left the WB for UPN last season; Angel stayed put — how did the crossover come to pass? Sources tell TV Guide Online that, because this is likely Buffy's last season and could be Angel's as well, the networks are giving wunderkind creator Joss Whedon the leeway to do whatever he likes. Gee, talk about a good news/bad news scenario!