What ram actually is that.. 'High Quality Grade Memory for Dell Laptops' ?

your XPS based 965PM, so the highest mem. speed it runs is 667mhz Max.
although if you go for pc26400s-800mhz, it'll still downclocks to 667mhz.

So, the best option you can pick is,
go for low-latency ddr2 sodimm, aka tight timings.
there are 2gb stick sodimm 667mhz rated @cl4
get 2 sticks of them and run it @ 2x2gb dual channel 667mhz cl4.

normal ddr2 sodimm-667, is rated @ cl5
so the LL kit with cl4 will have higher bandwidth thus better performance.
but do note that, the performance difference between both is very minimal.

yea, you can go for the hyperX if you'r rich enough & want the best out of it.
using xps m1730, shouldn't be any problem with $$$ lar

here u go, the low-latency 4gb kit
kingston hyperX KHX5300S2LLK2/4G
pre-programmed JEDEC @ 667mhz 4-4-4-12 , so just slot it in it'll auto-runs at that profile without any tweaks.

normal sodimm-667 runs at 5-5-5-15.

already answered on post above.
however it does shows a solid few hundreds MB/s of increment in bandwidth through everest benchmark.

i dunno bout the price, but i can say it's surely much more expensive if compared to value sodimms.
(but if don't compare, then it's not really that expensive lar.. since all ram ddr2 ram price drop kao kao! )