Does installing the clockworkmod recovery require rooting galaxy s2?
In general, no you should be able to install CWM with needing to root, but most of the tutorials I have seen for the S2 GT-I9100 involve rooting the device.

Here are a couple links that may be of interest to you.  I do not think you will need to root to install CWM.  

As always, proceed with caution when flashing.

Galaxy S II GT-i9100 Install CWM &amp; Root

Samsung GT-I9000 Galaxy S CyanogenMod install: Flash ClockworkMod Recovery

INDEX of GUIDES/TUTORIALS: SGS2 GT-I9100