Can I just buy a chain and put it on. What's involved? Do I need to remove links for fitting? Is there a recommended brand?

Yes

Breaking the old chain or remove the rear wheel. Mock up new chain. Cut new chain to length. Put new chain on. Adjust chain tension. Lube new chain. Go ride.

Perhaps. Depends on the length of the chain. I removed a few but left my new one a little longer to keep the rear wheel further back. As the chain wears and stretches, you will need to readjust. I had to remove another link once mine stretched.

http://www.monsterparts.com/c/Chain-Sprocket/Chain-Sprocket.html

It's really not hard to do. Get yourself or borrow a chain tool and take your time. Remove the rear axle and don't lose the cone shaped spacer. Make sure it goes back in the correct orientation. Lube the axle when you put it back in. Use your foot to hold the rear tire when you are putting it back on. Torque the rear wheel to correct specs. Don't over-tighten the chain adjuster bolts. They will shear off.

Don't ask Ash for help either. You'll regret it...

I've already run into that cone spacer and did put it on backwards and had to take the wheel off to put it on correctly.  The only part of that description that has me  is "cut new chain to length". Whats involved? What does the chain tool do? Also at MonsterParts there are two different chains for sale with a $40 price difference. Whats the diff and which one should I get?

Oops just found the Chain Replacement link. I'll watch that but I still want to know which one to buy please!

Ask and ye shall receive

What bike are we talking about here?

2005 620

Can't remember if I got mine from CA Cycleworks or Monsterparts. Either way you will be in good hands. Count the links on the chain you currently have. Order one that is identical or longer and cut it to to length.

520 pitch

Here is another link

http://www.ca-cycleworks.com/products/final-drive?p=3

But whats the difference between the two EK chains at Monster Parts ... MVXZ vs. SRX... besides $42.

Beats the hell out of me. I bought the more expensive one, replaced front and rear sprockets and rode the piss out of it.

No problems yet.

Yeah it looks like my rear is a bit worn at the teeth I think I'm going to replace it. Looking at the JT Steel at Monster Parts. I've already ordered the JT 14T front sprocket. Should I stick with the same number of teeth on the rear for my 2005 620 or change? I dont do any track just country roads, city streets and highway. I checked out the gearing commander link and its cool but I dont know enough to derive what I want from that online tool. Looking for a recommendation.

I just put a 14/40 combo on my seven fiddy. I left it with the local shop to rivet the chain tonight (cheaper than buying a chain tool). I'll report back tomorrow.

Yes you CAN replace only the chain but it'll wear faster. It's best to do chain/ sprockets at the same time. I went 15/43 on my gearing (M750). Going 14 in front is more popular but that's a little harder on things from research I did on TOB. I have about 2 sets of tires on mine (not sure on mileage) and not a bit of problem.