You can get the source code of specific versions by giving the corresponding tag (for available tags see selector "--Branches--" here). E.g. the source code of version 0.9.1:
cvs -z3 -d:pserver:firstname.lastname@example.org:/cvsroot/qpegps
co -r v0-9-1 qpegps
If You omit the "-r versionTag" You'll get the latest CVS snapshot (which contains the latest unreleased features but is probably highly unstable).