I've come across a glitch that occurs when rendering certain materials in SW2004/PW2. I'm not aware of the range of materials, but I've found it evident in all of the ?Polished Wood' materials. It seems that anywhere the material crosses a ?Plane' the rendering exhibits a funky parting line. This will occur at both the part and assembly levels, which can get quite annoying. I have found however, that there is a way to resolve this until the bug can be corrected at SolidWorks. I believe the problem has been reported to SolidWorks by my reseller. If not, I hope somebody there reads this.
Some materials ended up with a default ?Surface Finish' set to ?Rough' and the ?Scale' pegged at 2. In the instance of polished woods it would seem obvious that you don't want some whacked out rough finish. One of two things will work to resolve this problem. If you're not interested in a rough finish ? set your surface finish to ?None'. If you need a rough finish, try not to exceed 0.5 (which is pretty massive anyway). This has cleared the problem up for me anyway.