for ex. is SAMSUNG PC2700s-25331-c DDR 1GB laptop RAM compatible with one made by a different company and also is it okay to put two diff sizes of ram in the same computer?


Answer:
As long as both sticks of RAM are DDR and the right pin set it is fine to have two different brands, and yes you can have a 512mb Stick in with a 1GB stick its fine.

Answer:
Yes, it will work. Both sticks will operate at the speed of the slowest stick.

Answer:
As long as both are DDR and PC2700, you should be fine.

Answer:
They should be fine.