can i replace 200 pin ddr sodimm ram with 200 pin ddr2 sodimm ram?

hello everyone,

so im considering upgrading my Aspire 1800 laptop by increasing its ram.

it has 3.2ghz cpu
128 ati radeon x600 gpu
but only 512 mb ddr1 sodimm ram (PC2700) but as i understand it it can support up too 2 gigs.

i looked online and found that both ddr and ddr2 sodimm ram have versions with 200 pins but ddr2 is nearly a quarter the price and four times as fast.

i have a dell pc tower with only 2.8ghz cpu but it has ddr2 ram so it seems weird to me that a more powerfull technology uses an older ram technology. there are both Pentium 4.

so should i buy the ddr2 or ddr1?

thanks a lot for your help/knowledge.