There is a recent thread that AMD will no longer be producing A64 CPUs in s754 after June 15th - only the Turion, Mobile and Sempron will still be produced in s754. Since you don't upgrade often you should be good with a s754, but take that tidbit of info into consideration when making your final choice.
Make your mobo choice on what features you will need/use, price, performance and customer service from mfr. What other components are you thinking about using in the system? What will the system be used to for; gaming, video editing, music, internet, etc.? Will you be doing any OCing? Again, i would go with an nVidia chipset, either the the nF4 or the nF4 Ultra. I really like the performance and features of the
<A HREF="http://www.newegg.com/app/viewProductDesc.asp?description=13-136-152&depa=1" target="_new">DFI Lanparty UT nF4 Ultra-D</A>, but you may not need all of the features/performance of that board. Here is an <A HREF="http://www.anandtech.com/mb/showdoc.aspx?i=2337&p=2" target="_new">Anandtech DFI nF4 review</A>. Another option is the <A HREF="http://www.newegg.com/app/ViewProductDesc.asp?description=13-127-197&depa=1" target="_new">Abit AN8</A>. Great product by a great company.
Here is a link to a bunch of <A HREF="http://www.nforcershq.com/modules.php?name=News&new_topic=45" target="_new">nForce4 Reviews</A> and a little dated <A HREF="http://www.behardware.com/articles/531/page1.html" target="_new">s754 vs s939 review</A>.
Do your research and make an informed decision when deciding s754 or s939...
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