Is it allowed for Muslim followers to attend Christian church services or is Obama a Christian contrary to popular rightwing propaganda?

Time Magazine
For the past five months, White House aides and friends of the Obamas have been quietly visiting local churches and vetting the sermons of prospective first ministers in a search for a new — and uncontroversial — church home. Obama has even sampled a few himself, attending services at 19th Street Baptist on the weekend before his inauguration and celebrating Easter at St. John's Episcopal Church.
Now, in an unexpected move, Obama has told White House aides that instead of joining a congregation in Washington, D.C., he will follow in George W. Bush's footsteps and make his primary place of worship Evergreen Chapel, the nondenominational church at Camp David.
A number of factors drove the decision — financial, political, personal — but chief among them was the desire to worship without being on display. Obama was reportedly taken aback by the circus stirred up by his visit to 19th Street Baptist in January. Lines started forming three hours before the morning service, and many longtime members were literally left out in the cold as the church filled with outsiders eager to see the new President. Even at St. John's, which is so accustomed to presidential visitors that it is known as the "Church of the Presidents," worshippers couldn't help themselves from snapping photos of Obama on their camera phones as they walked down the aisle past him to take communion.
The challenge of not only being part of a church community but also praying in peace has long been a problem for Presidents, according to historian Carl Sferrazza Anthony. "McKinley hated having people staring at him while he read Psalms, sang hymns, put money in the collection plate or took communion," he writes in America's First Families. "By the 1920s, getting a presidential family in and out of church was a production. Secret Service agents had to cordon off a clear path from the curb to the church entrance before the Coolidges arrived ... [and] they were swiftly escorted to their third-row pew."
The Clintons attended Foundry United Methodist Church on 16th Street, and were particularly active during the years before Chelsea left for college. But White House aides say that security measures required by the Secret Service have become stricter since 9/11 and would cause significant delays for parishioners — and at significant cost to taxpayers — on Sunday mornings. Given Obama's popularity within the African-American community, the President also worried that if he chose a local black congregation, church members would find themselves competing with sightseers for space in the pews.
The First Family won't have that problem at Camp David, where the 150-seat Evergreen Chapel attracts a congregation of between 50 and 70 people most Sundays. The rustic stone-and-glass octagonal structure was built nearly two decades ago through private funds; President George H.W. Bush dedicated it in 1991. At the ceremony, Christian singer Sandi Patti sang and the late Cardinal James Hickey of Washington delivered a sermon calling the chapel a "witness to our common belief that we need to seek divine guidance in the conduct of our national affairs."
Each week, regardless of whether the President is on-site, Evergreen Chapel holds nondenominational Christian services open to the nearly 400 military personnel and staff at Camp David, as well as their families. A music director from nearby Hood College coordinates adult and children's choirs (Clinton sang occasionally with the choir when he visited). In December, the kids in the congregation put on a Christmas pageant and the chapel holds a candlelight service on Christmas Eve. The Bush family enjoyed Christmas at Evergreen Chapel so much that they celebrated the holiday there for all eight years of Bush's Administration.