I agree the matrox card has issues with hardware, so I would onlt go for authorised boards. it may be worth going with the Matrox and trying it, if it isnt stable then you still have the software, and with a Dual Xeon system, the mpeg encoding should be pretty quick.
Premiere doesnt have a HDV plugin yet, but virtually all software will in the next few months. As far as i am aware, Pinnacle Liquid Edition 6 and Canopus Edius 3 are the only platforms that accept HDV. However you can always down convert the HDV to DV, as the quality is still much higher than standard DV, whilst the HDV plugins are being developed.
As far as graphics cards go then it wont really help unless you are doing much 3D work, or you go down the Pinnacle Liquid route as you can specify GPU effects, but generally anything half decent should be fine.
Hope this helps.
Intel P4 2.6GHz
80Gb(System) + 2 x 200GB(Media)
Avid Xpress DV, Encore, Audition
Plus - P4 2.8GHx, 1GB RAM, DVR 108, Geforce FX 5900XT