2x1gb dual channel vs 2.5gb single channel

[audiophan]

laptop:compaq c762nr

this being a budget laptop i'm looking for a minimal investment. which option would be recommended, price being similar:

2x1gb sticks replacing the 512mb modules or
2gb stick replacing one 512mb module and keeping one

i have limited knowledge to dual channel. in the second option, will 512mb of each stick be in dual channel or will each stick be in single channel mode.

 

[Delerious]

Thats my question as well for my desktop. going from 2gb dual channel to

1. 4gb dual channel (will cost $35)
or
2. 3gb single channel (will be $15)

 

[Marty502]

I'd always priorize memory size. Even more so in a laptop with a (generally) slow hard drive.
Memory bandwidth isn't important in everyday tasks, unless you do heavy video editing often.