it's sometime I click back or home.. it turns to the HTC logo & my home screen start loading like reboot.. anything happening? it's function well nothing wrong with it after all.. just wants to know what happen on my desire.. & this time I click back.. it goes home screen & my wallpaper turn back to the bubbles wallpaper.. stock wallie.. & i trying to set back my HD rare black wallpaper but it doesn't work.. how & what should I do?

sifu's here~ i really cant tahan the Laggy cause by less of memory & any others lack of feature on my desire~

i wish i could root & flash it~
i do rooted my cousin Galaxy S to different firmware & ROM

but still i'm not so clear about rooting & stuff on my desire~

1 very important question i wanna ask is:
can i unroot it back & send to HTC for warranty claim after i root my phone??
(cause sometimes it will reboot itself but rarely happened... just scare there's something wrong with it, & need to send for RMA at future ><")

any link to refer?? wat did you guys do on ur desire?? root it?? flash it??