Your computer shouldn't stop you from downloading *.xls (Microsoft Excel) files even if you haven't got Excel loaded on your computer to read them with.
What is your method for attempting download?
In Internet Explorer, you right-click the file's hyperlink and select "Save Target As..." (then selecting a place to save it to).
In Firefox, it's similar, but the instruction is "Save Target As...".
You can get a free Excel reader application at the Microsoft site: "Excel Viewer" is a free download at
http://tinyurl.com/dys2vh.
Hope this helps.
JNPS (by later edit):
The line about Firefox should have read:
In Firefox, it's similar, but the instruction is "Save Link As...".