在820万条目表中的一个条目上选择一个varchar字段 - 性能帮助

I have a table with 8.2 million entries in a SQL Server 2005 database. This table stores basic past customer details (referrer, ip, whether they entered via an advertisement, etc) for every customer we have had come to the site. Unfortunately, whoever designed the table (way before I was here, I'm a lowly intern) used a I have a table with 8.2 million entries in a SQ