Many THANKS for emacs !

At the moment I try the X version (to shorten the learning curve).

Problem :
( N810, OS .43-7 )

Font size does not change with the font menu under Options.
"Font not found" appears at the bottom line.

When I type "emacs" in Xterm I get:

Warning: Cannot convert string "-*-courier-medium-r-*-*-*-120-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-medium-r-*--*-120-*-*-*-*-iso8859-1" to type FontStruct

Have I messed up my installation ?
Should fonts be installed separately ?

Thanks for any help !