Ok, well being that the Lamp is this old and cant be tested, you should order it and replace,
How long does a DLP projection lamp usually last?
It is safe to list the lamp life for most DLP front and rear projection televisions between 1000 and 2000 hours. I know that's a cop out, but it's hard to nail down a direct length of time. Some lamps might last only 500 hours while others may last 3000 hours. The window is so broad because no one knows for sure how long one lamp will last versus another. They're like light bulbs, and depending on how you use them, some will just last longer.
To put it simply, if you watched television three hours a day the lamp would last approximately 333 days at the 1000-hour lamp life and 666 days at the 2000-hour lamp life. That's pretty realistic because most people will want/need to replace their lamp every 1-2 years, but there are stories of people replacing a lamp every 6-8 months or every 3-4 years.
How do I know when it is time to replace my lamp?
Trust me, you'll know. The screen will lose its brightness and appear dim. You won't necessarily have to replace the lamp when you notice the dimming. Some people might wait until the bitter end to install a new lamp while others will have one in reserve waiting for the screen to dim. It's a matter of choice.
How much do replacement lamps cost?
Unfortunately, replacement lamps for all projection televisions are costly - in the over $200 range. Depending on the type of lamp and manufacturer, the cost will vary considerably. Where can I buy a replacement lamp?
I suggest contacting your manufacturer to see what lamp they recommend for your particular television, and to see who is an authorized dealer in your area (if any). There are a lot of good online stores that can send you a lamp usually for a lower price, but I would be a little wary about ordering something fragile like a replacement lamp through the mail. My concerns are that the lamp would be damaged in shipping, and the online retailer might be difficult (a rare case) to work with regarding replacement of the replacement lamp.
Are they easy to install?
My answer is yes, but I must qualify that by stating it all depends on who is doing the installing. Some models of televisions might be more difficult than others. Usually, it should be as much or little as twisting a screwdriver, pulling the lamp out, inserting the new one, and turning the set back on. This is definitely something to ask about before buying your television.