i got PCMCIA modem Sony Ericsson GC79. on mandrake and mandriva every thing was ok with connection. but i wanted to try Slackware. i install Slackware 10.2 with kernel 2.4.32 - no frendly form my modem - so i tried to compile new kernel with .config from my old Mandrake kernel 2.6.8. every was ok with compile. but now when i tried to connect by pppd with my GPRS-network provider i got:
ttyS4 no such device...
how to compile kernel?

p.s. sorry for my english... is wery bad;] - i'm from pland;]

You can use the .config from one kernel as a .config for another. You should however go through the configuration to verify that everything is as you wanted it (make menuconfig - for example).
I doubt that this approach will give you good defaults though when doing what you did - taking a .config from a 2.4 kernel to configure a 2.6 kernel.
Too much has changed between these for this to "just work"
Do: "make menuconfig" (or "make config" or "make xconfig") and check that pcmcia and the driver for your card is compiled in or a module - which you need to load somehow of course...
Or maybe you just picked the wrong ttySX ?