Mix, match DDR 400 and minimum overclock for 3700+

[usegobos]

I bought a 512 stick of corsair XMS a couple of years ago....

http://www.newegg.com/Product/Product.asp?Item=N82E16820145416

and now I have upgraded my system to a gig of this...

http://www.newegg.com/Product/Product.asp?Item=N82E16820145450

Is there any reason why I shouldn't use these two together. I would like to make sure that there isn't a small detail that I am overlooking.

Also, is there a no-brainer, minimum overclock for an 3700+?

Thanks

Al

DFI Lanparty n64 Ultra-D
AMD Athlon 64 3700+
1 gig Corsair XMS DDR 400
eVGA 7800 gt