Historically, when you wanted to connect to an Oracle database you could not get around downloading and installing a bulky Oracle client.
Since 2 years already an alternative exists: Oracle Instant Client. This is the marketingname for a zipfile with all DLL’s necessary for connecting to an Oracle instance. The zipfile is 30MB, and the unpacked size is about 70MB (one of the DLL’s is a hefty 61 MB!!). The installation guide tells you to create a directory and place this directory in you PATH environment variable. It’s better to put it in your %systemroot%\system32 (e.g. c:\windows\system32) directory (which is really all you have to do), so you do not have the need to extend your PATH variable.
For users requiring SQL*Plus it’s possible to download install those libraries separately. In fact, al you need is the sqlplus.exe executable.
Oracle Raptor (the still-very-beta alternative for TOAD) appears to use an instant client mechanism too. It doesn’t need any clientsoftware after all. And bytheway, Oracle has just renamed it to Oracle SQL Developer. Lately you really need to pay attention on the OTN site, because project names do change often nowadays.
Download Instant Client here.
Download Oracle Raptor here. (Early Adaptor Release 6 at the time of writing)