Processor advice needed please

Hi,I need a little advice as to whether it's worth to upgrade my rig.First let me tell you what I have now... P4 2.8 (old 533 bus), Intel 865PERL motherboard with 1 gig DDR (333mhz ) running in dual paging mode with an ATI850pro 256gb AGP card.OK now.. I have to get a new processor/motherboard for the wife.. due to failure... due to budget limitations I cannot get anything too expensive.Here is what I was planning... Intel P4 640 on a cheap motherboard with 1024mb 400mhz ram. Now my questions are based around... is it worth me keeping the new hardware? ( and giving the wife my old stuff for her simple uses - outlook/word etc. )Would I see a worthwhile increase? My old processor is NOT Hyperthreading...the new one would be...plus a little faster.Any thoughts on dual paging of memory... ??? If I spend more on a processors..then less is available for a decend motherboard. Does RAM operating in dual mode really increase speed much?Is it better for me to get an Athlon64 3200? My long term plan is to buy a killer system for me at the end of the year... DX10 capable for FSX... but this has come up... and I am pondering the idea.Maybe I should give the wife the new hardware so she can get better performance from her outlook express- LOL.Any thoughts most welcome...Thanks.Paul