Dịch - Finnish-English - Muistathan

sijaishakemusesi is not placement

That's right. Placement means having a temporary job for gaining work experience.

Sijainen instead is a substitute, also temporary, but only because the regular employee is unavailable because of illness, for example.

... your placement application (to be a substitute)....
electronic registration system of substitutes...
(There can be another registation for permanent jobs.)

This term is used exceedingly rarely in Finland, via google search I found 4 matches for sijaishakemus.

You can also search for the uncomposed words "sijainen hakemus".

I did, zero results. That's why I said it's used exceedingly rarely as a compound word or as individual words. The typical Finn would probably be perplexed by this one.

I have doubts here on
-placement (my dictionary would lead me to say "application for locum-tenency" or "application for being a substitute"
-supevisor (superior or boss)
-having been to placement interview (it means: having taken the interview in order to be included in the substitute register // having taken the interview required for becoming a registered substitute)
-electronic registration (it really is a calendar which is made available for personnel in the intranet)
-don't translate the name of the street
-start (free interview times start)(why not: there will be free interview....)
-date in English f.ex. January 5, 2009
-you need to use "please" with "-han" (muistathan, poistathan)
-also I guess more polite in English would be to say "you may reserve an interview..."

"our address will be the same" I would prefer.