I have an old Thinkpad 755c that uses the same video chipset. 
You might try XF86Config:

http://thinkunix.net/unix/os/linux/XF86Configs/wd90c24-tp755c-debian30r1


On Tue, 8 Feb 2005 09:10:46 -0600, Chris Schumann <cschumann at twp-llc.com> wrote:
> > Date: Mon, 7 Feb 2005 15:04:04 -0600
> > From: Jim Crumley <crumley at belka.space.umn.edu>
> 
> > On Mon, Feb 07, 2005 at 01:31:33PM -0600, Chris Schumann wrote:
> > > I'm a Red Hat and Fedora user so far. But now I have an old
> > > laptop (486) that I want to get running. Debian seems OK, but
> > > the XFree86 is lame (320x200).
> >
> > 320x200 ?  That's odd.  If that's your main problem with Debian
> > on the laptop, you might want to search for a better XF86Config
> > for it.  Does the laptop have a CD drive?  If so you might want
> > to try Knoppix, which sometimes does a better job of configuring
> > X than Debian itself. Just boot up Knoppix, and copy the
> > XF86Config to your Debian partition.
> 
> The issue is that the laptop has the WD 90C24 chip. The svga driver
> (or that portion) was not ported to XFree86 4.x and the package has
> no maintainer.
> 
> The generic vga driver is being used, so that's limited to 64k
> video memory with 1 or 8 bits per pixel, and 256k with 4. My machine
> has 1024k video memory, which is enough for 640x480 at 24bpp.
> 
> The old laptop is an IBM ThinkPad 750P. It has no CD-ROM at all.
> I can network with it, but that won't let me boot Knoppix.
> 
> I'm also limited by the 36MB of RAM in it right now, which I just
> upgraded on Saturday to that maximum level.
> 
> At least Linux can see and use the 12GB hard disk in it.
> 
> 
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