Dual head video cards

[dgmm]

Are there any "gotchas" I should look out for when purchasing a dual head 
video card?

I'm currently looking for a cheap NVidia card with both analogue and digital 
output to use my old 21" CRT and the new 19" LCD but, as usual, there's very 
little info other than for Windows in the write ups/reviews.

I've never used dual head before so I'm concerned that some cards might share 
resources to the extent that they are windows only .  Maybe I'm seeing 
potential problems that aren't there?

Budget is tight so I don't want to screw up the purchase.  "Cheap" is word I'm 
looking for :-)

-- 
Dave