You can use any skt 478 mobo that will accept P4 at or above yr processor GHz rating.
Your existing RAM should be fine unless you want to upgrade.
Word of caution: make sure yr case will accept the mobo. Most mobo's and Cases are industry std but the
likes of Dell,HP etc tend to use non std made for them. Also make sure yr PSU is suitable. If any doubts buy a new case & PSU.
Try here for mobop's click here