the only way i know of changes the red , close window and maximize minimize buttons
If you want to change the size of the taskbar icons themselves and make the taskbar smaller it is the same option as changing the red x for closing windows size, in win 7. thats control panel>personalization>window color>advanced or something like that(my themes are turned off the selection changes) or start(windows circle)>run > C:\Windows\System32\rundll32.exe shell32.dll,Control_RunDLL desk.cpl,Advanced,@Advanced
use: Caption Buttons , default-cutoff is 18 for normal size at 17 all the icons become tiny
im not sure of the default but 18 looks correct.
changing things in that properties dialog window will make windows 7 never look the same again so PLEASE use EXTREME CAUTION CAUTION CAUTION those settings can really do a job on windows, need a reboot afterward, dont do with more than 1 or 2 windows open etc...
its definate pen and paper material before changing anything write down what you change, dont use the apply button only use cancel or ok so you can revert back by cancel, the apply button is certain death.