I have the same sound card and it works beautifully with ALSA's snd-es18xx driver.
You can get this module with an ALSA install ... i believe when you 'make' you have to say something like '--with-cards=es18xx' (not sure about that ... see the README for that); OR you can compile it as a module with your kernel. I did the latter with kernel 2.6.6 (not sure if the es18xx driver is included with earlier versions) under Device Drivers -> Sound -> ALSA -> ISA devices ==> Generic ES18xx driver. Check it as a module and save the config file. Then 'make modules' and 'make modules_install'.
You should have the snd-es18xx module on your system now. Run 'alsaconf' to probe for your card, say yes to probe legacy devices. It should give you an option to probe es18xx .. check it and probe. When alsa is finished, it may or may not have found your card...it didnt for mine (i can't see my snd card with lspci, nor if i do 'pnpdump'). Nevertheless ALSA had modprobe's the sound driver so go ahead and see if the card works. If it does, then just add 'modprobe snd-es18xx' to your /etc/rc.d/rc.modules file or edit /etc/modules.conf appropriately.
Hope this helps