For a Dual Channel config. check the following,
1. Both modules are the same capacity (e.g. both are 256MB, or 512MB)
2. Both modules are the same speed (e.g. both are PC2700 or PC3200)
3. Both have the same number of chips and module sides (e.g. both have the
same number of chips on the module, and both are either single-sided or
double-sided).
if u still get blue screens then download memtest86 from
www.memtest86.com and make a bootable cd and test each of ur ram sticks one at a time for 3-4 hours and see if u get any errors. if u get errors then get ur ram replaced.