Find out what your home is worth now and get an estimate of what prices have appreciated in the past ten years and work backward. Itsn't an exact science, but it will put you in the ballbark.
here's just a handful of what came up ...check the web reference I have linked.
For the area roughly bordered by: 405 to the west, I-90 to the south, 520 to the north and Lake Sammamish to the east (isn't exact, but close enough for now), the median sale price of single-family homes in January 1998 was just under $249K ...a whopping 46 units closed (that were listed with the NWMLS). In Feb '98, the median sales price was $220k, for march, $250k, april was $255k, may was $250k, etc. etc. ...it hits a high of $268k in August, and closes the year out at around $242k. This is just the entire area as a whole and really doesn't say much about your specific house.
I'm curious why you're trying to figure out what your house was worth nearly 10 years ago.
I would suggest contacting a Realtor or an Appraiser. Depending on if you are looking for market value versus tax value etc. will play a large part in determining the information you are seeking. I could suggest a Realtor in your area that works in your area if you need a contact person. When trying to find an estimated value of your home for years past I think you will have to rely on a professional rather than trying to do it yourself as you will not be able to access the past information as readily as an appraiser or a Realtor.