Do the Verdana or Tahoma fonts exist on Linux?

No Linux has no Verdana nor Tahoma fonts.
Some Linux distributions (e.g.SuSE)  alow you ( after accepting MS Licence agreement) to connect to MicrosoftWEB sources and download Microsoft proprietary fond of True Type Fonts  (TTF) which will then be included in font sources  directory so your fs ( Linux font server) can use them.
Anyway you can cpy TTF files in your fonts directory but then you have to manualy edit and configure font server for X system which can lead in troublesome opeartion if you're not familiar with editconfig Linux.

more info and workaround you'll find here :
http://linux.org.mt/article/ttfonts
http://www.idautomation.com/kb/unix-finst.html
http://corefonts.sourceforge.net/

  "... try to make sure any web content I code works in multiple browsers "
   Whatever font type you chose in your HTML code the way fonts are displayed on screen  depends on browser configuration. Verdana and Tahoma fonts would  be most likely replaced by Beatstream Vera fonts on Linux boxes. Mozilla browsers ( Netscape and Firefox) will default to adobe-courier-iso8859-1 or adobe-helvetica-iso8859-1 and  beatstream-courier font that are closest mach to Verdana/Tahoma  TTF fonts.

good luck
nedvis

nedvis,
  You design a webpage and ask every visitor to download those fonts?

Yes , mgh_mgharish , I use to  design webpages and here is the one I'm most proud of : http://www.geocities.com/svstevandecanski  ( with Serbian cyrilic fonts) created - belive it or not with Mozilla Composer .
Or my personal home page : http://www.geocities.com/n_visnjic
No , I DO NOT FORCE  visitor to download fonts .
My answer was NO LINUX HAS  NEITHER VERDANA NOR TAHOMA font. These are Microsoft proprietary fonts and if you want to have them installed you can download and install them as you wish.
By my best knowledge only Xandros Desktop and SuSE linux distributions have that feature ( download and install Misrosof TTF} But unfortynately Microsoft discontinued support for WEB fonts . More info here : http://www.eu.microsoft.com/truetype/fontpack/win.htm

good luck
nedvis

You see.. it is not a good idea to rely upon the user to download the fonts if he has to view the page... instead you should use most generic fonts
For ex..

http://www.prajavani.net/feb162005/home.php

Here they have used some "Kannada" language fonts. Can u see that? So moral is to use generic fonts available on all platforms than to use some remote or unknown fonts..

OK.. Let me assume that the fonts are downloadable..
But will the users be aware of the thing that they should download that font to view the contents correctly?

"...But will the users be aware of the thing that they should download ..."

NO THEY WONT! .Average user cannot care less for WEB fonts - the only thing he/she is interrested in is CONTENT.  Average user DOES NOT KNOW EVENT HOW TO INSTAL ADDITIONAL FONTS IN WINDOWS!!!
 If they cannot see the content at first attempt they will give up and go somewhere else.
And I agree , use most generic ( better yet standard fonts) and  dont  worry about  page "visibility" .
Sure if you know ell your targe sudience you'll probably try to meet their system capabilities.
I didnt code my church WEb site for Bulgarian or Russian but for Serbian cyrilic and I KNOW ANYBODY RUNNING IE6 and MOZILLA BASED BROWSER CAN  SEE CHARACTERS CODED IN UTF-8 FORMAT.

nedvis
   

I agree.. But not Verdana or Tahoma