Not done it, but can give some pointers,
Volt Meter:-
+ve, you can wire this up to the ignition switch (the wire that becomes live +12V when at position II ,normal running position, don't wire it to the +ve terminal from the battery as the gauge will be on all the time), you will probably find a spare terminal (spade) on the switch for this type of thing.
-ve, you can wire this up to any ground point (usually black wires attached to metal parts)
Oil pressure gauge:-
this really depends on the sender, does your engine have a pressure sender? or just a temperature switch? etc
for the gauge to work the sender needs to have variable resistance with pressure.
the -ve terminal will go to any ground in the instrument panel
the +ve terminal will go to the sender.
does this help at all?