Yes you can. My wife put it on her Dell and it worked fine.
http://exo-blog.blogspot.com/2007/11/update-re-testing-vista-w2gb-ram-office.html
To use Microsoft Office Small Business 2003, you will need:
* PC with Pentium III, 450 MHz or higher processor
* 256 MB of RAM or above recommended
* 380 MB of available hard-disk space.1
* Super VGA (800 x 600) or higher-resolution monitor display
* Microsoft Windows 2000 with Service Pack 3 or later, or Microsoft Windows XP or later operating system
http://www.microsoft.com/smallbusiness/products/office/sbe/default.aspx#Evaluate