The following is a sum total of knowledge at my disposal regarding the apparent Alternate Reality Game PostExpression.

The current stage has brought us to the website commsforspirits.com, meaning Communications for Spirits. As of 2200 Greenwich Mean Time June 25th, 2006, the site has changed to show the following image located at http://www.commsforspirits.com/i/pe_june25.gif.
The image present is a person standing on top of a raining cloud with an antennae. Clearly a mediaglyph of the text present in the image: "Death Ends A Life, Not A Relationship", "Communications for Spirits", "This changes life, and death, online".

Within the HTML source of the website, the following is commented out: "pe_pamiabftcs". Major props to LacrimaWanders for pointing that out - my source browser opened small, and I was unaware any notation occured below the closing HTML tag. A little savvy and experience with the previous stage of the ARG yields an image located at commsforspirits.com/i/pe_pamiabftcs.gif, it's message is "Pluck a message-in-a-bottle from the cyber sea."

Here is where progress on the stage peters out. The index page for commsforspirits.com/i has "tut-tut" commented out of the HTML source, but there is no indication if this is intended to obfuscate the location of commsforspirits.com/i/pe_pamiabftcs.gif, or some other image whose name we must guess.
Proceeding along various lines of inquiry in line with the first stage of the ARG. There may be a .txt file. That hypothetical .txt file is not, apparently, named after any of the images on the site. The /i subdirectory is the only one that returns an index.html page, any efforts to solve the problem should at least be tried in this directory.

Postexpression.com purports to be a new community that is in beta-testing phase. The site is owned and presumably operated by Mike Wrafter (DNS /whois), someone well-versed in online web-based games like The Beast, that served as a promotional entity for the then-new Steven Speilberg movie A.I., and spawned the Cloudmakers group.

The site was announced at www.wrafter.com on April 10th (no link avaliable, no cache avaliable except for the Google.blog heading info), and the domain name was registered on the second of June. A friend pointed out that April 11th was the day the Cloudmakers started up - a somewhat tenuous supportment of the this-is-a-web-game hypothesis. Additionally, the following text is contained in the html of the PostExpression website, because of course people think that there is a game involved! The banner postexpression.com hosts is so darn obfuscate of purpose: "Looking Here Won't Give You (M)Any Clues, But Nice Try"
Who is this, Al Gore?

There is an option to register to be in a "second wave" of membership. Those one hundred in the first wave recieve an altered banner image (but not a hosted image, all instances of the image I have found have been imageshacked, not deeplinked) that denotes their status.

To learn the rules of the "game", you need to sign up at the site, and then click the HERE button on the page following data input, this takes you to the rules page.
Offhand, this looks like little more then a device to spread the word about a new community. A bit of looking around the Internet reveals that people like the banner, but have no idea what the Hell postexpression.com actually is.

Updated 6/19. At Mark Wrafter's website. Highlight the image to get a message. Go to the image directory to find a txt message here. This has the same message as the one hidden in the .gif image, but with "Comms for spirits."
Brief google search turns up Commsforspirits.com. There is a .gif there that cycles animation once. It nominally says "Extra time in the game of life." and flashes "Return June 25th 2006."

Phase 2 here.