The minimum cpanel will run on - 256mb ram.

I dont suggest you install kloxo on 128mb ram, as there wont be any ram left for anything. Let alone kloxo.

Webmin is your ideal panel if you want a panel, otherwise 128mb should be fine for a tiny startup site or even a static site - you should tweak your vps to get the most out of it, and I suggest no panel, and install services manually.

Best of luck,
Cheers,
Ryan