I am confused on this issue.  Although the Dell specs state 4Gb max and 1Gb per slot, as other replies have confirmed, Dell also sells a 2Gb module (Kingston Part# : KTD-DM8400B/2G, Dell Part# : A0767525) specificially listed as being compatible with the Dimension 9150 and XPS 400: 

<ADMIN NOTE: Broken link has been removed / replaced from this post by Dell>

Guess I'll have to buy it and see if it works.  Anyone tried these?

i have the same computer w/ 4 512mb pc2-4300 (ddr2 533) chips, and one just failed, so i need to upgrade and saw the same thing on the dell site just now, tho w/ corsair.  so did you do this? if so, what is the result?  if not...anyone, what would be the fastest memory upgrade possible here? whether 4-1 gb or 2-2gb sticks ...both are rated 800ghz..will it run at that? thanks!

chris, thanks for the quick reply. on the corsair page it seems to only show the 533 mhz stick, their vs1gb533d2.  and on the dell page the 1gb sticks are 800mhz, only the 512k is 667.  so is it correct that the 9150 can't run at 800mhz?   and is it possible to order th u8622 dimm running at 667 that you list above? and it will it run at 667? ( i assume so, but i don't see it as an option on the corsair page.)

addendum: i just checked the crucial page and it seems to show that 4-1gb sticks running at 667 is the max (tho they also show an 800 offering from 'ballistix' that the reviews indicate only will run at the slower speed).  it does seem that to  run at 667 that i'll have to upgrade all 4 of my 533 chips, i.e. get 4 1gb at 667 to max out, correct?

I had to return the memory.  I spoke with a technician and confirmed that the 9150 only supports 4Gb max, so I sold the 9150.  It is disappointing that Dell hasn't yet corrected the site; the technician I spoke with agreed that the site was incorrect and said he would submit information to get it corrected.  That was nearly 2 months ago.

Six months later, Dell still hasn't corrected the site.  I wish I had found this thread *before* ordering the 2GB sticks.  (I wish even more that Dell had not recommended the incorrect memory in the first place or at least fixed the error when it was first reported -- very disappointing.)

Pm

The Dell Dimension 9150 will support 2GB modules, up to 4GB max. You can only use two 2GB modules. I have one sitting on my desk right now with one 2GB module installed and it is running fine. If you are using two 2GB modules they must be installed one the same channel (both on the white slots or both on the black slots).  If you install them on separate channels, or install more than 4GB RAM, the system will not boot.

I am disappointed that a Dell representative replied to this with incorrect information. The max memory config is 4GB, but it is not limited to 1GB sticks.