I'm using 2.6.0alpha2(x86) now.
http://forum.doom9.org/showthread.php?t=149113
but that RawSource.dll is for 2.5.
2.6.0alpha is completely compatible with 2.5.6 or later.
If you want to develop for 2.6 or later, then see manao's code.
http://forum.doom9.org/showpost.php?...&postcount=473
it includes 2.6 header file.