DX3D8 Game Engine, 30 Years later, help

I have been assisting my learning disabled friend to make his dreams come true!
But after all this time spent developing this program (with great success- we thought we were done!)
We hit a snag that has raised a lot of questions, and we wondered if some expert could help us answer this mystery.

He doesn't learn new languages or APIs very well at all, so we had to stick with VB6 and DX8.
I heard talk of 'overhead' and wondered what that meant until we tried to render a .X file scene with 140K polygons and 90 texture maps.
It seemed that it had rendered faster before, but now proceeds at a crawl.

There must be a difference in the way Mesh.drawsubset(n) is called in VB6 vs. (for example) C
because the same mesh in meshview or other example programs --- that USE THE SAME DX8 FUNCTIONS
render much faster. Can somebody explain to us why that would be, and how we can rectify this issue?
Please have a care and avoid a quick answer pretty please....
We have examined (can't use) Truevision3D and BlitzBasic3D (both have free editions)

We aren't allowed to change the computer he uses and it's an antique W98SE system - but we've never
had a problem with it until today after crafting many levels and characters and artwork.
We'd love to hire an expert and could pay several hundred a month for an upgrade of some sort as well.
It is very important that we do not move or modify the computer he is using, so there's no quick solution.

Thank you for your replies,

J. Bockholt
Caregiver,
The Lynch Estate

I think you may be better off posting the question in the 'Games and Graphics Programming' section of the Fourms; that's where the Direct X gurus hang out and whilst your system may be old, I'm sure that someone will be able to guide you with respect to 'general tuning' the code for maximum performance.

I have reported this thread to be moved so you don't have to create new thread for the same subject.

Moved to the Games and Graphics Programming forum.

Thank you! I hope so. We'd love to place the final project as open source code here to benefit everyone. It is an engine that takes advantage of what we feel is most of the standard features DX8 has to offer, even fog. It would be nice to assemble something that would be useful to anybody who wanted to make a game or a movie of some sort. It loads .x files that have multiple objects, and even skinned meshes inside of them. The capability is there to even load .x file animations (though it doesn't do anything with it right now). An .ani file is separate and allows multiple animations to be applied to skinned meshes. We have a complete collection of hand-written macro files to export much stricter .x files from 3ds max 5. The comment fields in .x files for bounding squares (with altitude) allow for collision detection, directional sound placement, cutscene generation, music playing, variety of features. Could be tidied up a bit and have a C-based DLL-type of file to make it all work much better maybe. Collaboration would be welcome since this is for everybody. Credit given for an honest and helpful individual(s). Visual Basic 6 was the last language most like regular BASIC for those who can't handle syntax-intensive, somewhat cryptic mainstream language.