I've been using MovieWiz extensively for several months and am happy with the performance. My 800 movies are spread across 3 network drives and network performance has never been an issue, even with 100Mb/s connections.
High bit rate movies (HD movies) will place a high demand on your network performance. I'd check the playing the movies from a local drive to help determine where your bottlenecks are.
I like the SQlite database format because there are lots of good tools to fiddle with it if you want to "play".
I also use an UNC approach to movie paths and mainly modify my movie database on another system on my network.
Dedicated XP SP2 + GB-PVR 1.2.13
Gigabyte GA EP45-DS3L, Q6600 processor, 2GB RAM, SPDIF optical audio
Sapphire ATI HD4850 GDDR3 512MB PCI-E
DVico Digital Tuner
4TB local storage, Pioneer 107 DVD+/-RW via USB
Logitech 785 remote control, Logitech wireless keyboard and mouse
Antec Sonata II case & PSU
Sony 40in X2000 Bravia LCD, Panasonic 5.1 surround sound