Enabling Network on installed WordPress 3 and more

Ill try to explain my idea.

I have a running WordPress Installation (No network enabled yet) on https://www.landnet.se hosted at Binero.se

I also have two other sites hosted at one.com namely https://www.landweb.se & https://www.cestcui.se

Ive decided to move the latter two to binero.se. and close my account at one.se

I want to use all my domain names as before!

Question

Can I use different domainnames in a network(multisite) setup or
Should I just put them in different folders as separat installations and map my domainnames to each site?

Thanks Mike