XCC Mixer? IrfanView, MS Imaging, which comes straight with WXP, and various other programs can read PCX files. I recommend IrfanView, because of its extra inbuilt features.
Yeah, Irfanview is the best and easiest to use. It also won't bother you with too much PC resource hogging like other photoviewers and editors. It also supports many image filetypes, so you can batch-convert your screenies.