This model has a separate video card, so it is not necessary to replace the mainboard.  It's also not on the list of systems for which the warranty was extended:

http://en.community.dell.com/blogs/direct2dell/archive/2008/08/18/nvidia-gpu-update-dell-to-offer-warranty-enhancement-to-all-affected-customers-worldwide.aspx

The ATI cards are about $150, but that's probably not what you've got - they rarely fail.  The nVidia-based cards are more on the order of $500-600 or more.

Many thanks, ejn63 for a quick and informative response

Here's the ATI card:
http://www.parts-people.com/index.php?action=item&id=3813

Here's the nVidia FX Go 1400:

http://www.memory4less.com/m4l_itemdetail.asp?rid=fd_10&itemid=1440691958

i could not locate many nVidia Quadro FX Go 1400 graphis cards or the ATI Mobility Radeon X600 cards. These are as I know, the two cards to fit in M70 or D810's motherboard

Please could i have some help in choosing similar graphic cards wirh 128 - 256mb memory that is compatible with Precision M70.  many thanks in advance.

Many many thanks, ejn63.  finally managed to import the ATI card from parts-people and fixed and the M70 works like  dream once again.

Best wishes

RSJ