Unless you can get a 3.0GHz 478-socket real cheap, i.e. less than $100, then no.
Go ahead and upgrade to 775, try to get a 975X chipset as those SHOULD support the new Intel processors, the brand new Conroe! It shows promise, and trust me, it'll blow that 2.4 out of the water, and the best part: It is about the same clock!
I currently have a socket 478 celeron D 2.4. Should i upgrade to a socket 478 p4 3.0 ghz w/ht or switch to a lga 775 mobo with a lga 775 p4 w/ht .