BeatCleaver is an easy-to-use tool for slicing samples and loops. It can slice WAV, AIFF, MP3, and M4A/AAC formats, fluid zooming to the sample level, and the ability to slice by beats or bars given a fixed tempo. The Windows XP version is limited to slicing only WAV and AIFF files, however.
BeatCleaver for Windows XP is available now for $15 / €12 / £10, and as a free upgrade for existing users.
A free trial version is available on the Oscillicious downloads page.