Before rooting, be sure you are using the right rooting methods
There are at least FOUR different version of the 8.9 out there. Make sure the root method you choice works for YOUR tablets.
7300 Tegra 2 with 3g
7310 Tegra 2 with Wifi
7320 ??? with LTE
SCH-i957 ATT LTE version with Snapdragon processor
Root for the Galaxy Tab 8.9 7310 is very easy to do.
Galaxy Tab 8.9 Root - xda-developers
Then you have to flash a custom recovery
[RECOVERY][22.OCT.11] ClockworkMod Recovery v5.0.2.6 - xda-developers
After you root and apply a custom recovery you can finally flash a custom ROM with ICS. For the 7310 and the 7300 Tegra 2 models. There are two different BETA ROM's you could choice from. They are beta, they have a lot of work to do before they are at full quality but both of them are really smooth and give your ICS goodness albeit with some kinks. Camera not working is a huge issue. Hotspot on the 7300 is another big issue
The first one is an AOSP built specially for the 7310 model and it is the one i use. Version 1.4 has a restart issue but version 1.3 is solid for a daily driver
[ROM][ICS][AOSP]Galaxian-Soup[GT-7310/7300][beta 1.4][02.8.2012] - xda-developers
This second one is a port. The original ROM was a beta for the 10.1 wifi tegra 2 tablet was then ported over to the 8.9. It is just and functional if not more so in some cases. Its most recent version does not have a restart issue
[ROM][ICS][P7300/P7310]Unofficial CyanogenMod 9[2012-02-08] - xda-developers
i hope this help. The forums over at XDA are very friendly and i can help you here if you prefer.