I was looking for SP1a a while back and I was able to go from SP0 to SP2 first and then SP3. I have had SP3 complain about a .Net requirement that has to be satisfied before SP3 will take, of which the .Net update is part of SP2.
These days I have a SP3 slipstream fully patched to all but the last surprise patch that Microsoft released after they stated they were no longer supporting it. So its a clean build direct to the next to last patch and then 1 patch and done.
***Isnt the Core 2 Duo E6400 2.13Ghz and not 1.8Ghz. I went on a google search because I have an older system with the Core 2 Duo E4300 1.8Ghz and was going to compare the differences since I thought they were both 1.8Ghz and then I saw that mine is 1.8ghz and yours should be 2.13ghz if its a E6400.
http://www.cpu-world.com/Compare/586/Intel_Core_2_Duo_E4300_vs_Intel_Core_2_Duo_E6400.htmlMy Core 2 Duo E4300 was an upgrade I performed from the weaker Pentium E2160 in a Dell Inspiron 530S that was given to me. The Pentium E2160 lagged in comparison to the Core 2 Duo E4300 even with XP Home SP3 clean build. Now its faster with the Core 2 Duo.