3.4 cd version is not yet out , still working on it.
3.4? dvd needs a total of 20gb for linux , ie: 128mb /boot optional , +/- 1024mb /2048mb / 4096mb swap , and the remaining used for root partition. This ends up as total +/-12gb used in root partition including /home if you installed everything on the dvd. You would likely reuse the swap partition
You could get away with using less space / only select kde + p2p / internet and it should use a few less GB's of space. Mine avg's about 12gb inlcuing downloaded + installed + updated files in /usr/portage. Portage can grow to 1gb / 2gb / 4gb if not carefull / purged frequently.
Gparted should be able to resize your ubuntu just backup the info before doing it.
You can use virtualbox ontop of windows / ubuntu / osx or using vmware to run Sabayon in there if windows partition has more space and once used to Sabayon you can install it onto the hard drive.
PS> I have linked using live dvd 3.4a , a preformated empty 20gb ext3 .vdi image (download size = 1.5mb.rar) for virtualbox under the virtual pc part of the forums as this does save a lot of time by extracting the rar file after checking for viruses and repartition + install. Using the virtual hd creator it has to be "allocate space now" for sabayon or it would not work and allocating this space does take a long time + then formating it. Just use the 1.5mb .rar and extract about 10 to 20 mins extracting on normal speed pc. (growing space did not work for me last ime I tried)
Hope this helps.
Edit: SL 1.0 BE uses much less space and is ideal for virtual pc use , excludes games. viewtopic.php?p=49841#49841