The one you posted is 2005 1,33GHz 12" ibook G4. It came with a 40GB HDD. The fact that it has 20GB means it has been opened.
Leightweight in terms of weight or the work? This ibook weighs above 2kg.
Ibooks
http://www.everymac.com/systems/apple/ibook/index-ibook.html
PowerBooks
I would in both cases take the top of the line model, i.e. the ibook G4 June 2005 or Powerbook October 2005 mode.
Which you take; I would make this dependant on the size you wish (although despite the size, the PowerBook is more practical / leaves more options in my opinion).
In other words:
12" ibook G4 1,33GHz (mid 2005), 512MB-1,5GB RAM, min. 40GB HDD, ATI 9550 32MB, combo-drive
14" ibook G4 1,42GHz (mid 2005), 512MB-1,5GB RAM, min. 60GB HDD, ATI 9550 32MB, superdrive
15" (with high resolution) PowerBook G4 1,67GHz (late 2005), 512MB -2 GB, min. 80GB, ATI 9700 128MB, Dual-Layer-Superdrive (mind there is also a low resolution, non DualLayer Superdrive version from january 2005!)
17" (with high resolution) PowerBook G4 1,67GHz (late 2005), 512MB -2 GB, min. 120GB, ATI 9700 128MB, Dual-Layer-Superdrive (mind there is also a low resolution, non DualLayer Superdrive version from january 2005!)
PowerBooks alumminium, ibook opaque white.
As a compromise between CPU power and size you could look for a
12" PowerBook 1,5GHz (jan 2005), 512MB - 1,25(!) GB RAM, min. 60GB HDD (later shipped with 80GB), GeForce FX Go5200 64MB, superdrive
http://www.everymac.com/systems/apple/powerbook_g4/specs/powerbook_g4_1.5_12.html
but there is some debate among users, if the mid 2005 Ibook's Graphics card is beter than the one in that PB. However CPU power usually is more important for Macs, the 12" PB also has less RAM).
Also mind, that the dimensions of the books is somewhat misleading. The ibooks are something like 5:4 and the PowerBooks are 16:10 (the 12" ibook looks as if it equates the 15" PB in depth - I'll try find pictures of both beneath and on top of each other).
Mind, when shopping, that there are models with the same CPU frequenzy, but different allowed maximum RAM capacity! So be sure, you get, what you are searching for.
When you finally get one, test if they awake form sleep, if not the DC-in board can't hold ultra low voltage anymore.
OR
for the collectors and (even more) challenge thing the top of the line ibook G3 and PowerBook G4 (Ti) that are still OS 9 bootable. The reason some love them is that they can boot into OS 9 as well as Mac OS X.
See here
http://www.everymac.com/mac-answers...rt-faq/last-macs-to-boot-startup-macos-9.html
As an addendum for enjoyment
this is from 2010, but you can have a small insight what you can expect from a G4 ibook.
If not going for a PowerPC for collector's reason shop for the last MacBook that had Firewire.
