Regarding a PC that has an Intel E2200 (2.2GHz), can that mobo accept an Intel Core 2 Duo E8400 3.0GHz or a Intel Core 2 Duo E6850 3.0GHz with no problem?
 
Both the processors are 3.0 GHz but with a few different specs. The E8400 looks as though it has the upper hand:
 
E8400 LGA 775 65W Processor / 1333MHz FSB / 45 nm Wolfdale / 6MB L2 Cache  
E6850 LGA 775 65W Processor / 1333MHz FSB / 65 nm Conroe / 4M shared L2 Cache
 
Is the E8400 the fastest Dual Core that's compatable with a mobo with a E2200?
 
Thanks again!
Jamie

Check your motherboard's compatibility list. Sometimes it will take a BIOS update to make the new 45nm processors work. Sometimes they wont work at all. It just depends.
 
As for performance differences. Generally the E8400 series will run just as well as the E6850, but at a lower temperature from what I've seen. It doesn't seem to overclock any better.

I purchased the E2200 and overclocked it since I could not find an E8400 for a reasonable price. My mother board the DS3L will support the 8400 with a bios update. Any of gigabytes P35 chipset motherboards have support for the E8400 via a bios update.
 
http://www.newegg.com/Product/Prod [...] 6813128059
 
 
I believe the E8400 does overclock better. O know of no review site that reached 4Ghz on air with a E6850. The E8400 did reach 4Ghz on air however.

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3 more years to get my BSEE @ UNH
Intel E2200 @ 2.90Ghz (264x11) | 3GB DDR2 800 G.Skill (2x1GB, 2x512MB) | Gigabyte DS3L | Gigabyte 8800GT 512 @ 675/1566/900 | 160GB Seagate 7200rpm SATAII | Seasonic 500Watt SS-500ES | XP Pro

Your better off OCing your e2200 to 3.2 and waiting on a better performane upgrade like a quad or something else like better GPU.
 
The Cache doest mean jack to real world APPS, maybe a 3-7% improvement on synthetic benches. Almost all software isnt programmed for large Cache. I have a e2180 3.0 check this out:

 
OC to 3.2-3.3 and you will beat the e8400.
Now if you want to go to 4.0 then the e6750 or e8400 might be for you.

Knowing what motherboard you have is highly helpful.  As Sciggy suggested, check with the manufacture of the motherboard. Also, between the e6850 and the e8400, get the e8400 UNLESS your motherboard will only support the e6850.

Edit: You could also due what Roadrunner suggested. Just OC the e2200 to 3Ghz.

 
 
You should put that atleast on a 1333 FSB OC. Might need a after market fan but you should hit 3.2 as a given on stock cooling.

According to this link, it should support the E8xxx CPU's
http://h10025.www1.hp.com/ewfrf/wc [...] 37&lang=en
Thanks!
Jamie