The Hilton Portland (main building) is located on SW 6th Ave between SW Salmon and SW Taylor. The new Executive Tower's main entrance is located on SW Taylor between 6th Ave and 5th Ave.
The Hilton's home page provides directions and maps to help you get there, but the instructions below provide some additional details on how to get to the Hilton from the airport.
Light Rail
The cheapest method for getting to/from the airport and hotel is by light rail, and it's real easy. Portland's "MAX" is a new rail line that runs from the airport to "Pioneer Square" in the city center; the "Pioneer Courthouse Square (north)" stop is less than two blocks from the conference hotel (and note that Portland has short blocks, half the size of city blocks in, say, New York City.)
(MAX is part of Portland's public transportation system, TriMet, which you may want to use to get to other places while at ICSE. For details see the TriMet web site),
At the airport, the MAX terminal can be found on the baggage claim level, at the south end of the terminal (past Baggage Claim Carousel #2). There, you'll find schedule information and ticket dispensing machines. The fare to downtown is $1.55, and trains run approximately every 15 minutes. The first train to downtown leaves just after 5:00AM, and the last leaves shortly after midnight. The ride to downtown takes 30 - 40 minutes.
The MAX ticket dispensing machines require cash, but they accept and make change for $1.00, $5.00, $10.00, and $20.00 bills.
When you disembark from Max at Pioneer Courthouse Square (north), you'll be between 6th Ave and Broadway. On foot, make a right on 6th Avenue and go two blocks to the hotel's main entrance on 6th Avenue between Taylor and Salmon Streets.
(To see this last step on a map, go to the Hilton's home page, and click on "Local Maps" on the navigation bar at left. If you zoom in once, you'll see the Hilton's location, with the rail lines marked in red showing MAX, just north of the hotel. Pioneer Square is the green rectangle just north of the hotel and sitting between the two rail lines.)
You can repeat the above steps in reverse to get back to the airport; pick up a brochure in the airport for details.
Taxi Cabs and Town Cars
Taxi cabs and town cars are available outside baggage claim; these run by meter, and charge between $30.00 - $50.00, depending on how long the trip takes (i.e., depending on traffic) and with cabs being cheaper.
Hotel Courtesy Vans
The Hilton website is NOT correct, there is no longer a courtesy bus from the airport.
Automobile
From the Airport, take I-205 South and exit onto I-84 West. At the end of I-84 West, you will reach the junction of I-5 North & South. Head South toward Salem (to your left) on I-5. Follow the signs onto I-405. Take the 6th Ave exit off of I-405. Follow 6th Ave for 13 blocks and the front doors of the Hilton will be on your left-hand side.