Reported by James Dietrich on the Debian BTS on Nov 26th. He's using Debian Mesa 7.0.2 and a 2.6.22.5 kernel on
  VGA compatible controller: Matrox Graphics, Inc. MGA G400/G450

Mesa 7.0.2 fixed a crash of blender on mga (in _generic_read_RGBA_span_RGB565_MMX). Now, blender still crashes at startup, with a different backtrace.

Blender (2.45-1) crashes on startup in mga_dri.so:
guessing 'blender-bin' == '/usr/bin/blender-bin'
Compiled with Python version 2.4.4.
Checking for installed Python... got it!
/usr/bin/blender: line 46: 23243 Segmentation fault      blender-bin
"$@"

(gdb) bt full
#0  triangle_twoside_flat (ctx=0x8ad0ae0, e0=1, e1=2, e2=0)
    at ../../../../../src/mesa/tnl_dd/t_dd_tritmp.h:202
        vbcolor = <value optimized out>
        VB = (struct vertex_buffer *) 0x8b18948
        mmesa = (mgaContextPtr) 0x8acb1b0
#1  0xb68e4f4e in _tnl_render_poly_verts (ctx=0x8ad0ae0, start=0, count=32, flags=57) at tnl/t_vb_rendertmp.h:313
        efstart = <value optimized out>
        efcount = <value optimized out>
        j = 3
        tnl = (TNLcontext *) 0x8b18508
        TriangleFunc = (const tnl_triangle_func) 0xb6837580 <triangle_twoside_flat>
        stipple = 0 '\0'
#2  0xb68e60d6 in run_render (ctx=0x8ad0ae0, stage=0x8b18704)
    at tnl/t_vb_render.c:320
        prim = 3013300288
        start = 0
        length = <value optimized out>
        i = 0
        tnl = (TNLcontext *) 0x8b18508
        tab = (tnl_render_func *) 0xb6a0d260
        pass = 0
        __PRETTY_FUNCTION__ = "run_render"
#3  0xb68dd573 in _tnl_run_pipeline (ctx=0x8ad0ae0) at tnl/t_pipeline.c:158
        tnl = (TNLcontext *) 0x8b18508
        __tmp = 895
        i = 7
        mask = 63
#4  0xb6819e65 in mgaRunPipeline (ctx=0x8ad0ae0) at mgastate.c:1063
        mmesa = (mgaContextPtr) 0x8acb1b0
#5  0xb68ddaf1 in _tnl_draw_prims (ctx=0x8ad0ae0, arrays=0x8b06920, prim=0x8b0547c, nr_prims=1, ib=0x0, min_index=0, max_index=31)
    at tnl/t_draw.c:402
        bo = {0x80b6e32, 0x80b6e30, 0x8b06778, 0x0, 0x1, 0x403, 0x0, 0xb75a1a98, 0x80b6e2c, 0xb69870d1, 0x807bb24, 0x1, 0xb7f59ff4, 0x8b08518, 0xbfb35cb8, 0xbfb35cd4, 0x0, 0x807bb24, 0xbfb35cb8, 0xb7f5a7c4, 0x17, 0x0, 0x1, 0x0, 0x1, 0xb6819a11, 0x8aeca48, 0x8aecc50, 0xbfb35c38, 0xb688feab, 0x8aeccc0, 0xb6a0d1e0, 0x40}
        nr_bo = 0
        tnl = (TNLcontext *) 0x8b18508
#6  0xb68d66e0 in vbo_exec_vtx_flush (exec=0x8b05358)
    at vbo/vbo_exec_draw.c:215
        ctx = (GLcontext *) 0x8ad0ae0
#7  0xb68d21f8 in vbo_exec_wrap_buffers (exec=0x8b05358)
    at vbo/vbo_exec_api.c:80
        last_count = 32
        __PRETTY_FUNCTION__ = "vbo_exec_wrap_buffers"
#8  0xb68d2346 in vbo_exec_fixup_vertex (ctx=<value optimized out>, attr=3, sz=4) at vbo/vbo_exec_api.c:218
        exec = (struct vbo_exec_context *) 0x8b05358
        i = <value optimized out>
        id = {0, 0, 0, 1}
#9  0xb68d52b2 in vbo_Color4f (x=0, y=0, z=0, w=0.882353008)
    at vbo/vbo_attrib_tmp.h:163
No locals.
#10 0xb6964a23 in loopback_Color4ub_f (red=<value optimized out>, green=<value optimized out>, blue=0 '\0', alpha=<value optimized out>)
    at main/api_loopback.c:228
No locals.
#11 0x08139c04 in BIF_ThemeColorShadeAlpha ()
No symbol table info available.
#12 0x08178efd in ?? ()
No symbol table info available.
#13 0x00000021 in ?? ()
No symbol table info available.
#14 0x00000000 in ?? ()
No symbol table info available.

See the Debian bug for full lspci output and Xorg.log.