GA-P35 S3G vs. EP45-UD3 total amount of system memory...

[KWILD]

I've recently buy an EP45-UD3 coz i need more PCI-e slots for future expansions.
Well the system is the same i have with my old GA-P35-S3G (CPU q6600 @ 3000 MHZ,4gb G.Skill DDr2,ATI HD2400,2 x SCOPE PCI DSP audio cards,1 x UAD-1 PCI DSP audio card,1 x UAD-2 PCI-e audio card).
Well with the GA-P35 S3G i can get a total amount of 3,5 gb of memory under win xp pro sp3 (with or without /3gb /pae /userva switches).
With the new EP45-UD3 i got only 3GB of total ram!If i try the /3gb switch i got a lot of errors just when xp pop ups , lot of hard disk activity , lot of message errors and system very slow and totally unusuable.
Just to be more clear,when i check the amount of free memory under task manager (soon after the boot) with the older P35-S3G i can get 2,90 GB and more of free ram...now with EP45-UD3 only 2,60 GB.
I've also search for some functions into bios to enable PAE or memory remapping but i don't find nothing at all...
ANy clue?

[Conners]

I don't know for sure but I think some video cards use ram for them selfs. It also my be a difference in how each mother board recognizes it also.