What are computer stores selling computer components in helsinki and in Espoo ?
There are plenty of computer stores in the Helsinki metropolitan area. A few popular ones are Verkkokauppa in Ruoholahti and Jimm's PC store in Arabian kauppakeskus (Arabia shopping mall). The former is a well-rounded computer store with relatively good service and lots of staff to help you. The latter is a specialized component store that carries lots of high-end components for the more advanced hobbyist.
A great way to find the best value for your money is to use a web service called Hintaseuranta (rough translation could be Value Watch) provided by MikroBitti computer magazine. Hintaseuranta allows the user to search any given component and provides him with a list of stores that carry said product in prize order. The search can be narrowed down to show stores in certain area. The service is in finnish and thus some translations of terms are in order:
Tuote = product
Tuotehaku = product search
Hakusana = search term
Hinta = prize
Hintahaarukka = prize range
Alin hinta = lowest prize
Keskihinta = median prize
Kauppa = store
Korosta valitun seudun kaupat = bold stores in chosen region
Pääkaupunkiseutu = Helsinki metropolitan area
I hope this answer helps you to find the best bargain.