HNPCC means "Hereditary Non-Polyposis Colorectal Cancer," but being diagnosed with it does put you at increased risk for other cancers as well - most commonly cancers of a woman's reproductive organs, and less commonly the GI and urinary tracts. Because of that, doctors often recommend complete colectomy for anyone with HNPCC, plus a hysterectomy for women.
However, these surgeries are certainly not required and there are other options, such as aggressive annual screening (including colonoscopy, pelvic exam with transvaginal ultrasound, annual CA-125 testing, and urine cytology on an annual basis, and endometrial biopsy less frequently).
Take the time to talk to a genetic counselor and educate yourself about your options. Please keep in mind that the only way to 100% prevent colorectal cancer is a complete colectomy - but that screening methods are constantly improving as well. I know people with HNPCC who have elected to have a hysterectomy and complete colectomy, and I also know those who decided to undergo the increased screening instead of having surgery. The important thing to all of them is that they found out about their options and chose the one that was best for them.
You may make a different decision than others in your family who have been diagnosed, but that is okay. Regardless of what you do, just remember that it is your body and the decision is YOURS.