well you can flash a custom kernal which is not the same thing as a custom rom. if you don't have custom recovery right now, you'll want to download rom manager from the market. it's a free download. after dl, open it up and select flash clockworkmod recovery. let it run it's coarse (which means it'll probably reboot) and now you have a recovery and you have a way to back up your current rom/setting/apps etc. so you can have no fear of trying different things.
after the reboot and your phone is loaded, go back into rom manager and select backup current rom. let it run its coarse (it will reboot into recovery, backup everything, then reboot the phone again).
then go and dl kernal manager from the market (also free). after, open kernal manager, select 'load kernal list', and this should bring up a list of kernals. i would recommend x99kernal-Sense because i've used it and it works well. but whatever kernal you try, make sure that under the third category (android flavor) it says Sense and NOT asop. you must select a Sense kernal since you are on a Sense rom.
After deciding on the kernal, you can download/flash it directly from the app. should work like a charm.
now you have a kernal that allows you to overclock. in order to access the abilities though, you will need an app like setcpu (which is not free) which will allow you set your settings.
