If you're moving to Seattle for the summer, you're going to need a place to live. Where you should live really depends on a number of factors. These factors can be reduced to these 2 variables: cost, and 'fun'.
Cost: This is the most important for a lot of people. Luckily none of the Boeing factories are high-rent areas, so if you want to have less fun... you can find lots of cheap(ish) housing near where you work. These are usually less fun neighborhoods though. I personally have never spent much time after-hours in Renton, so I can't imagine there is too much to do down there (for someone my age). I don't know much about Everett... but lots of the Everett interns came down to Seattle to hang-out last year. Cost is directly proporational to fun. Higher cost = more fun, Lower cost = less fun. On my scale, I'm going to rate places to live on a cost scale of 0 to 10. 10=$300/month, 0=$1500.
Fun: If you're less concerned with getting cheap rent, then you're fun-o-meter is definitely going to go up. For rating the 'fun' of a neighborhood, 0="no-bars-or-anything-significantly-fun-for-5-miles", 10="walking-distance-to-extreme-fun".
[Format... Neighborhood Name:
Belltown: 0/10 - Right outside of downtown... this is the place to live if you feel like you're going to want to go to lots of bars with lots of young people. Expect HIGH rent in this area.
Lower Queen Anne: 1/9 - (AKA "Uptown") A little past Belltown, this is a mini-Belltown. Not quite as many bars and restaurants, but still fairly "hip".
Upper Queen Anne: 1/7 - This is actually where I live. Its a little pricey to live on top of Queen Anne. But its a pretty good quite neighborhood that is only a $10 cab ride to Belltown.
U-District: 8/7 - This is where the University of Washington is. So, during the summer there is LOTS of housing, but not quite as many people there. You can usually find a place for about a 8-ish price. There is plenty to do in the U-District, and lots of good ethnic food.
Fremont: 3/7 - Self proclaimed "Center of the Universe". There are lots of good places to eat and drink at. It's got some nice views of the water (Lake Union).
Greenlake: 6/8 - I love Greenlake. Its a little recreational mecca within the limits of the actual city (I think). There is a beautiful lake with an awesome jogging trail around it. Good bars and good food.
These are the places that I go with some regularity. I don't feel comfortable commenting on the other neighborhoods around town. But, there are LOTS of websites with info about where you want to live. The MOST useful (that I've found) is this site from the Seattle P-I. Read it and soak in the information.
Go forth and find a place to live.