>>>I'd like to do a dual boot.

Yes you can. When you start your installation Linux will tell you that he found another system and ask if you want to keep it.

Then when you are done with the installation, Linux asks you if you'd like to install a boot loader, and if you would like to dual boot, and choose the default system.

>>>Unfortunately my laptop's only got a single hard drive and it's only got half a gig of ram. Will this be ok?

Yes, that will be OK. I recommend that you choose an X windows manager that have low memory usage like Icewm.

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