ive got the exact same chipset as you tana and had my problems too but here's how i solved it...
first of all the sound card is detected as a sis under windows(7018 if im right) but in linux it gets detected as a trident soundcard(lspci does give sis 7018 but alsaconf said it was trident) so in your kernel configuration(i prefer menuconfig) you must look under device drivers ---> sound ---> advaced linux sound architecture --> pci-cards and then search for the trident module then you can choose to make a module of it or you can compile it into the kernel (i prefer the latter).
then again there is something you must take in mind alsa 1.0.5 works with kernel 2.4 but alsa 1.0.8 doesn't (with me it didnt) it does work fine with my new 2.6 kernel. hope this helps

youri

I had the same problems
the best way is the recompile alsa modules in kernel