Can I transfer/copy info from one sd card to another.
Essentially lets say I had an old 2gb sd and just bought a 8gb. Can I transfer/copy data to the new one.
Lets say I have 2 different cards with stuff already on them. Can I combine the 2 cards into one.
As for copying from one card to another: yes. As long as you keep the same directory structure in tact, the system won't even know it's a new card other than seeing more free space than before. I've done this a dozen times over my Wii and 3DS systems.
Merging them into one, you may need to be more careful about. You need to make sure you don't have any duplicate information that would result one one overwriting the other in the copy process.
But if you had one SD card that contains only game saves and WiiWare, and another SD card containing only homebrew apps, then yes: you can combine both into one SD card, keeping their respective directory structures in tact within the new card, and you can use the card for both purposes at the same time.