Folding Bikes - Bike tuning

I've owned a Downtube FS 2005 for a few years now.
This year I've finally started putting it to more use than 3 rides per year, as I now regularly ride it to the gym as well as around the neighborhood.
Initially when I got it, I have tried to adjust for smoother gear shifting, and have only made things worse. Generally I am not a big fan of taking a bike to a mechanic, as it's supposed to be a rather simple device that anyone should be able to fix, and I have fixed/assembled plenty when I was a kid.. but now that the gears are getting jumpy, i either need some educational material on the matter, or just take it to a bike shop.

so 2 questions
1) can someone point to some useful links if I want to try by myself again (one thing I recall from DYI is that the shifting would not be the same upside down vs bike's normal position.. guessing some gravity is taking effect)
2) if my pathetic attempt fails, what should I expect/ask/pay at a local bike shop for a tuneup, and can I expect one done within 30 mins, as I plan to ride there.

Thanks in advance.

P.S.
The only upgrade to the bike I made was a brooks saddle.

http://www.parktool.com/repair/

Is this a hub geared or der bike?

How was the bike stored? Is there any rust on the chain, or stiff links?

My usual advice when a bike is not woking is:
1. Clean
2. Lube
3 Then look for poblems (adjust or new pats).

If the bike has not been used much dirt and old stiff grease plus rust can make a lot of problems, also if it does not look like a lot. Remember the cabels/housing. If some lube innside the housing makes the whole thing much better maybe it s time for some new cabels & housing. Water innside the housing makes the cabels rust, and no ammount of tweaking and adjusting is going to help.

Also folding the bike is hard on the cabels.

Tell us about your result!

Keep the bike supper clean and dry, lube and

Netcomrade, my avatar appreciates yours.

It's a der bike. The bike was always stored in a dry place and there are no signs of rust at all. The cables appear OK, I think some greasing and adjusting the der is all I need. I found a couple of links a on Downtube side, but your reference rules.
http://www.google.com/search?hl=en&client=firefox-a&rls=com.ubuntu%3Aen-US%3Aunofficial&hs=82E&q=+derailleur+site%3Adowntube.com&aq=f&oq=&aqi=

Replace the shifter cable. Shouldn't cost more than $15 including parts. May not fix everything, but it's going to help.

I adjusted the dérailleur and it seems fine now. Can't say it shifts like a clock, but much more satisfying.
The front bearing does have some side movement to it, i'd say less than a 1/4 of an inch, is that normal?

http://bicycletutor.com/

Clean what is dirty

Lube what moves

check screws

invest one hour a day at http://www.parktool.com/repair/

in less than a year you will have more knowledge than the average bike mechanic.

congratulations on your decision to ride your bike more often by the way.

I adjusted the dérailleur and it seems fine now. Can't say it shifts like a clock, but much more satisfying.
The front bearing does have some side movement to it, i'd say less than a 1/4 of an inch, is that normal?

Not sure what you mean, pix or better description is needed, but no bearing should have that much play.