motherboard?

how do you tell what kind of motherboard you have without opening up your computer and looking

What do you mean kind? Programs like cpuid or sisoft sandra will tell you what cpu, ram, etc you have, which is the info on your mobo that you need for most issues.

i right now have a p4 1.4 ghz and i wanted to get a new p4 3.0ghz, i wanted to know what kind of socket my motherboard has to make sure i can put it in

Get one of those programs. Its possible, there were both socket 423 and socket 478 1.4 P4's. If you have socket 478, you're in business.

make sure your mb supports the same fsb as any new processor you buy or it won't work. If you bought the pc as a package then you could check the manufacturer's website and it may have details on the hardware of your system (if its not too old). If it is quite old i'd guess you'll have to upgrade board for a 3ghz cpu. If you do end up havin to open the case the manufacturer and model no. is usually between the pci slots somewhere.