XF86_S3 strange behavior

Hi Debian users.   I have noticed that the XF86_S3 server makes strange things in the middle of the screen. Actually the window frames in that area (this doesn´t happen when close to any of the sides of the screen) appear jagged. Something like this under an augmenting lense

XF86_S3

Hello ! I need to configure a Miro Crystal PCI card with S3 SDAC (more exactely S3 Trio32/64 PCI) When I run xbase-configure and get the chip card menu, it says that running first the server /usr/X11R6/bin/XF86_S3 is required before configuring. OK. But, where do I find this XF86_S3 bit of