Sorry, but I agree with Troy. You'll be in a world of pain with Linux if you think you're having problems running Win 7.
You never mentioned what hardware you have Windows 7 installed on. I'm guessing, because you state that you don't have a CD or DVD drive, that you're using a netbook. These are not powerhouses. ANY modern operating system is going to make your hardware look, feel and work in a clunky way if it's not up to scratch. Inadequate processor power, memory and I/O all contribute to a poor experience, and it's not a fault of the operating system. No OS manufacturer is going to promise infinite backward compatibility for old hardware forever. Going Linux will not (necessarily) change that. It may even exacerbate it. Driver support has always been a major weakness.
Judging by the way you've asked your questions so far, I'd really not feel comfortable recommending Linux to you. It is not a "noob" OS, by any stretch of the imagination. Easy to install and use, if everything works right - yes. Easy to diagnose and get around hardware problems and compatibility issues - no.
If you do decide to dabble with it, I'd recommend Linux Mint - launched as a variant of Ubuntu with really well integrated media codecs. It's the closest thing I've come to so far as a simple but beautiful desktop Linux distro. Well worth a look. It's really well sorted, and is as close to a "noobie" offering as there is in Linux terms. There's no way around you having to get hold of an external DVD drive - or external hard disk that you can boot from. The whole point of doing this is that the computer runs from the external boot disk while it installs the new operating system on your internal drive. You can't install an operating system over itself while its running the machine... makes sense huh.
http://www.linuxmint.com/index.php