I want to now which ram is used for dell latitude 640, latitude 520, latitude 430, latitude 420 and inspiron 2200 is it ddr2 or ddr1 and max capicity for upgrade

Here are the max memory and speeds:
Lat C640 is Max 512M per stick DDR-266 (PC2100) or DDR333 ( PC2700 ) for a total of 1024 Meg

Lat D520 is either 2 or 4 Meg total. DDR2-667 ( PC2-5300 )
Although the memory can be installed one module at a time, the best performance comes from using matched pairs of modules.Maximum memory for systems with the Intel 945GM chipset is 4096MB, maximum memory with the Intel 940GML chipset is 2048MB
Lat D430 has only slot with a Max of 1 Meg. You can use DDR2-667 (PC2-5300)  or DDR2-533 (PC2-4200)

Lat D420 is a max of  1.5G    . Use 1GB DDR2-533 (PC2-4200)

Inspiron 2200 is one slot with a max of 1280 Meg. recomended is 1GB DDR-333 (PC2700)

Here is a link to find almost any memory you need:
http://www.crucial.com/index.aspx

NOTE:
When mixed speeds in the same PC, the memory will run at the slowest speed installed or the highest speed allowed by your system, whichever is slower.

Good Luck