How safe is it as a web designer to assume that
msttcorefonts would have beeb installed on a client machine viewing my website? If not what sans serif fonts should I use then? (for body)
No, Microsoft's core fonts are typically not included with Gnome or KDE installations.
You can use
Consider font embedding:
If you don't like that option, I agree with danlefree's suggestion of using
Alternatively, I just use similar fonts (in shape, etc) that are told to be common in most distributions, and of course, they come in font-family tag after Arial or verdana or whichever I want windows users to see , so linux users will see the alternative ones instead.
For a clue, I (I use mostly san serif fonts, similar to arial, verdana, etc) tend to set these : Nimbus Sans L, FreeSans, Bitstream Vera Sans, Liberation Sans, Dejavu.
Anyway, I set always first those fitting better my design, as many linux do have those as well (often Arial, verdana, etc)
You have here a relation of most common fonts in linuxes, udpated last february.
Last note: You might be interested in having an vmware virtual machine in Windows for trial and error in using these alternative fonts. I do this quite often myself. (we at Bitnami have VMWare virtual machines with Drupal or other CMSs already all set and configured)