You check the BIOS version by entering the BIOS at system startup (press the F2 key), the verion is listed on the first BIOS screen.
The custom DSDT is at;
http://acpi.sourceforge.net/
Building a custom kernel is not that hard, but you should do some reading before attempting the first time. This holds true for installing a custom DSDT also. Check out The Linux Documentation Project for HOW-TO's for both;
http://www.tldp.org/
My Acer Aspire 5000 is an AS5002WLMi-100GB running a custom 2.6.14.3 kernel with a custom version of CentOS-4.2.