BOSTON trip in March-what reasonably-priced hotels do u recommend & which is the best area of city to stay in?

I'd like to stay somewhere not too expensive but nice, comfortable & safe. Does anyone recommend any "MUST-SEE" tourist stops I should NOT miss?; what about easiest mode of transportation - subway, bus, cabs? Is it safe to walk at night? Any other ideas are welcome!
Thanks to my first answer I decided to mention I'll be traveling with a friend; we're both in our early 30s and we'll be going the last week in March.

Since I live in the Boston area, I haven't had much need to get a hotel room in the city. That being said, though...

I don't know your age, so I'm not certain what would interest you, but a couple nice hotels can be found in the Kenmore Square area...the Hotel Commonwealth is very nice and is right in the heart of Kenmore Square which is the heart of Boston University and a great club scene a block away on Lansdowne Street (adjacent to Fenway Park).

You should also consider hotels across the Charles River in Cambridge, which will put you close to MIT and Harvard. The Royal Sonesta in Cambridge is great...close to the Science Museum and good food. Further up is the Hyatt Regency which is right on the river but a little off the beaten path. There is also a Radisson with a great tepanyaki restaurant that is a favorite of mine.

Stay away from downtown Boston hotels especially in the Financial District. They're mucho expensive and the sidewalks are rolled up after 7 PM, so walking is not a completely safe bet.

Like any city, parts of Boston are safe at night and others are not. The Theatre District is fine when there are shows at the theatres, but it's unfortunately near what's left of the "Combat Zone", the adult entertainment district which is shrinking over time, but is still pretty scuzzy with hookers. Faneuil Hall Marketplace is the "tourist trap", but the food choices are endless (and no Boston visit is complete without a meal at Durgin Park). The Comedy Connection is a great night out.

Boston is a highly walkable city by day because everything is so compressed. But the streets are not laid out in a grid so the walking can be a little convoluted...be sure to have a walker's map. The MBTA (subway and buses) is reliable. I'd avoid the cabs unless otherwise stuck.

Places to visit: If you like to shop, Newbury Street is the place to be. The Museum of Fine Arts will suck up the better part of the day. If the weather is good, plan a few hours for the Arnold Arboretum ("The Arborway") for peaceful walking. Good walking also along the Esplanade of the Charles River from the Harvard bridge to the Hatch Shell, again if the weather is good.

History buff? Take the Freedom Trail walk from Boston Common. It's a self-paced trek.

Baseball fan? Take a tour of Fenway Park. Inexpensive and a lot of fun.

Italian food? The North End has the BEST in the
USA, and I'm not kidding. You have to go to Italy to get better and more authentic.

Just outside the city proper is the Bunker Hill Monument. You'll need a couple bus rides to get there.

Harvard Square is a bustle of activity...shopping, food, history. Another highly walkable area.

I've kinda rambled on about a few different things, but here's a tip to help you find things to do and see: take a ride on the Duck Boats. It's a good way to get a feel for the city, and the tour guides tell you what's worth exploring in more detail.