You can't reuse the RAM - it'd DDR2 - get some 1.5v low profile DDR3 1600 RAM.Because you are building this summer wait and see what the new z77 mobos and Ivy cpus are like. Will be a lot more choices for hardware by then.
Today's equivalent will include:
a. sandy/ivy bridge quad, likely the ivy bridge 3570K, due end of April.
b. A Z77 based motherboard.
c. a stronger 28nm graphics card. If your budget is $500 for a GTX680, that is as good as it gets. Lesser cards from amd are available.
Single cards will be so much stronger by the end of the year that I see no need for the extra expense of planning for sli.
d. 8gb of DDR3 ram in a 2 x 4gb kit is the new norm. Ram is cheap, get more only if you will run 64 bit enabled apps.
e. A SSD for the os and some apps. 64gb is about minimum, 128gb is much better. Use your WD blue for storage and overflow. Prices on SSD's are dropping, expect to
pay about $125 per gb. Intel 520 or Samsung 830 seem to be the best.
The case, psu, dvd and even the hard drive can stay.