can DCOUNT use formulae for it's ranges?

I am using =DCOUNT(database,field,criteria)

No problem but I would like to use a formula for the 'database' , 'field' and 'criteria' parts something along the lines of.

=DCOUNT(CONCATENATE(a1,":",z1),VLOOKUP(x,y,z),CONCATENATE(b2,":",z2))

but all I get is a #VALUE error message

is there a universal rule about not being able to use formulae where excel is expecting a name or range?

I use Excel 2000 on NT