It depends what word processor they have.
If they use OpenOffice or LIbre Office (both of which can be installed on Windows), then they can open it without any problems.
If they use an up-to-date copy of Word 2007 or newer, they can also open .odt files created in LibreOffice. However, Word 2003 and older cannot open these files, and many businesses still use Word 2003.
However, if you are using any kind of word processor file format, make sure you choose a font which is installed by default on Windows. If you do not, your CV will most likely come out in a different font on Windows, and it may look odd. (E.g. it might spill onto an extra page, or there might be odd spacing, or the substitute font might be a really unsuitable font, etc.)
A PDF is a safe bet, because nearly every computer has some kind of PDF viewer software. PDF is also good for making sure the formatting comes out how you expected it to. It is possible to embed fonts in a PDF file, too. If you do that, your CV should look exactly as you intended it (however, if you are going to rely on embedded fonts, make sure they actually are embedded - test the PDF on a Windows system that you know does not have your font installed (try the local library's free computers)).
That said, your choice of font should be subtle. A font with too much character will often appear unprofessional. If you are into typography, and if you can be certain that your CV will display in the font you choose (i.e. the font is embedded in the PDF), it would be worth selecting something which, to the untrained eye, would appear equivalent to Arial or similar and not make itself known, but which is actually a better-designed font which is easier on the eye. It should not be obvious to the reader that the font is unusual (unless they are also into typography), but they should still find the CV more attractive as a result.
If you are not into typography, it's probably best to stick with one of the MS Core Fonts, or a font that is very similar to those. If you use a word processor file format rather than PDF, definitely use a MS Core Font to make sure it displays predictably on Windows.
Some companies run all CVs through a piece of software that extracts key words and things like that. Make sure the plain text of your CV makes sense on its own if you strip away all the formatting. Don't store text in images either. If you are familiar with web design, this is quite similar to making a web page accessible to text only browsers, screen readers and search engine spiders.