If space is an issue then LAME supports ABR, which is like VBR, but the file averages out to be the equivalent size of a CBR (e.g. ABR 192 will be the same size as CBR 192).

Question : why would you want VBR (or ABR like you say) files with the same size as CBR files???
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Riocar 80gig S/N : 010101580 red
Riocar 80gig (010102106) - backup