if you have smallish word documents to convert and don't want to take the time to do it yourself the filament service can really be nice ; you just log in to your account, and when you connect the eb1150 using the usb cable and go to your online bookshelf, it will see the filament books site. however you do have a lot less control that way over the formatting, and there are limits on file size etc.
you can also make your own imp format books using the eBook Publisher program which is another free download from ETI. i recommend you download the manual (which can be found here as an imp book) and keep it next to you while you're working, because it's a rather steep learning curve. alternately, you can make mobipocket books and convert them in about 30 seconds using mobi2imp. for most books this is fine, although eBook Publisher is overall a more powerful program and allows you more control and better formatting, especially if you have some knowledge of html and css.
whatever you choose to do you can find plenty of help and advice here.