So you like the Custom ROM you been using and still want to try the new ROM which might be useful for you. What to do? Either re-flash your device and add the new ROM to replace the old ROM ( Duh!! annoying! ) or just install Boot Manager to dual-boot your Android device.
Boot Manager, is a nifty app in the Android marketplace which does what its name suggests. It allows you to choose which ROM you want to use while booting up. This App allows you to add and try up to three custom ROMs which it stores and runs from your SD Card, now of course this won’t give you the best performance as it runs from your SD card but you can surely try out the ROMs you always wanted to test/try.
Right now the app is officially supported on the original Motorola Droid, Droid Incredible, HTC Thunderbolt, HTC Vision, HTC EVO 4G, HTC Inspire 4G, HTC Desire, and the HTC Desire HD. It may work on other phones, though, they just aren’t officially supported yet.
For a detailed guide on how to install and use it, head over to Lifehacker.com