Well, Docky is. Uses 20MB RAM max, and like 2% of the CPU max. Avant has the tabbed system that you're looking for, but uses more CPU power.
In terminal type in sudo apt-get install avant-window-navigator
Here's my Docky, simple and light.
STABLE OCed AMD Athlon 64 X2 4200+ (2.2GHz to 2.7GHz stock voltage)
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