Oasis star Noel Gallagher wasn't too impressed after meeting Katie Holmes backstage at the US talk show Letterman. The 44-year-old singer slammed the Dawson's Creek actress, 32, on his blog over the weekend. Noel seemed excited to meet Tom Cruise's wife in the New York studio but felt snubbed after the encounter. He wrote: "We literally bumped into that top Scientologist Katie Holmes on the way into the studio. We came out of the lift and BANG, there she was." Noel and his pal Scully were so…