Anyone using the first beta of Microsoft Corp.'s Windows NT 5.0 will probably have real trouble using the Internet Explorer browser included in the operating system until Microsoft fixes a bug that sometimes prevents the software from correctly locating Web sites. PC Week Labs has confirmed that the browser has intermittent problems converting domain names (such as www.pcweek.com) into their corresponding IP addresses. When the bug occurs, IE either sends users to incorrect IP addresses (resulting in completely mislabeled pages) or simply times out, stating it is unable to find the site in question. In our tests, this problem did not affect the just-released version of IE 4.0, nor did it affect IE on operating systems other than NT 5.0 Beta 1, which has only been distributed to developers. All other TCP/IP utilities on NT 5.0 (including ping and FTP) worked correctly in PC Week Labs' tests. Because the release version of IE 4.0 is not supported on NT 5.0 Beta 1, we recommend users switch to Netscape Communications Corp.'s Navigator for all Web browsing until Microsoft fixes the problem. We tested Navigator 4.03 on NT 5.0, and it worked perfectly. Microsoft confirmed the problem and is working to find a resolution. The suggestions it posted to an NT 5.0 support newsgroup this week did not, however, fix the problems PC Week Labs encountered. We were notified of the problem when a reader mailed in a screen that, on first appraisal, looked as if Microsoft's browser was preventing its users from accessing Netscape's home page. After further investigation, however, it turned out that the problem was not specific to Netscape-Internet Explorer was presenting the home page of MCI Communications Corp.'s main backbone name server, ns.mci.net, as Netscape's home page. We saw the same buggy behavior when trying to access MCI's corporate home page and the home pages of several universities, as well as some pages on Microsoft's own site. Typing IP addresses (instead of host names) directly into Internet Explorer allowed us to reach the correct sites.