Terminais Gráficos: Problemas com o X

Há tempo venho tentando configurar algumas máquinas antigas pra funcionarem como terminais X. Já utilizei o LTSP, o Remote Boot da Conectiva mas em ambas o problema é o mesmo. Não consigo fazer as danadas funcionarem em modo X.
Segui as recomendações do Morimoto no "Entendendo e Dominando o Linux" mas na hora de startar o X nos clientes surge a mesagem:
_____________________________________________________________

(WW) CIRRUS(0): Default mode "1600x1200" deleted (insufficient
memory for
mode)
(WW) CIRRUS(0): Default mode "1600x1200" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1792x1344" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1792x1344" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1856x1392" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1856x1392" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1920x1440" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Default mode "1920x1440" deleted (insufficient memory for
mode)
(WW) CIRRUS(0): Mode pool is empty
(EE) CIRRUS(0): No valid modes found
(II) Unloading /usr/X11R6/lib/modules/libddc.a
(II) Unloading /usr/X11R6/lib/modules/libi2c.a
(II) Unloading /usr/X11R6/lib/modules/linux/libint10.a
(II) Unloading /usr/X11R6/lib/modules/libvgahw.a
(EE) Screen(s) found, but none have a usable configuration.
Fatal server error:
no screens found
When reporting a problem related to a server crash, please send
the full server output, not just the last messages.
This can be found in the log file "/var/log/XFree86.0.log".
Please report problems to xfree86@distro.conectiva.com.br.

_____________________________________________________________

O que será que tenho feito de errado ?