Advent 8215P Laptop RAM upgrade help....?

i bought this laptop a few weeks back and i need to upgrade the RAM from 1 to 2GB because its running Vista. However, the site i bought it from and Advent's own site are completely useless and dont tell me anything about the RAM spec; all i know is its DDR2, but im not sure what speed. If someone could help me here so i dont go wasting money buying the wrong RAM would helpful.