For one thing, since you are not Orthodox, you can not receive Communion in the parish (we practice closed communion). But please enjoy the services nonetheless.
Unfortunately, due to circumstances beyond my control, the only Holy Week services I've attended are Holy Friday, Holy Saturday and of course, Pascha.
Holy Friday is very humbling. Words alone can not describe it enough.
As for Pascha, services usually begin at 11:30pm Saturday night. Pascha is the feast of feasts. One of two times of year that I look forward to most (the second being Nativity).
The Pascha service lasts about three hours (don't worry, it goes by
fast) with a procession around the church building, lots of hymn-ing and of course, the Paschal Sermon of St. John Chrysostom (can be read here:
http://www.oca.org/FSsermons-details.asp?SID=4&ID=10)
Again, words alone can not describe Pascha. It is truly the greatest feast of the year. Of all the churches and services I have been to, Pascha is the one that most affirmed to me that God is truly present in the Orthodox Church.
It has also been a year since last Pascha and my recollection right now is a bit slow. So I'll try to describe afterwards.
At the end of the service, usually around 2 or 3am Sunday morning, we have one of the largest foodfests you could ever lay eyes on. The Fast (we fast from meat, dairy, fish, wine and oil - wine allowed Sundays) is over and we all "break it" together.
After this, people will either go to their houses for sleep or some will stay at the church. Around noon time Sunday, we all go back to church, hear the Gospels and so forth. The Gospels are read in different languages by the faithful. To use my parish as an example, we heard the same Gospel first read in English by the deacon, and then in Russian, Ukrainian, Old Church Slavonic, Japanese, Norwegian, Greek, Swahili, German, Arabic, Spanish, French and Latin (though not necessarily in that order).
Afterwards, when the service is over, we have a huge foodfest.
Other than that and without going into too much detail, all I can really say is come and see.