Sorry, you don't need a pair of G400's.
The dual head is so called because it has 2 ports and can drive 2 monitors at the same time... =)

Jazz
(List 112, Mk2 12 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)
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Jazz (List 112, Mk2 42 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)