The IE7 can't be started. In the debuglog the following exception can be found:

16:19:11.296 INFO [11] org.openqa.selenium.server.SeleniumDriverResourceHandler - Command request: getNewBrowserSession[*iexplore, http://localhost:8080/, ] on session null
16:19:11.296 WARN [11] org.openqa.selenium.server.BrowserSessionFactory - running in proxy injection mode, but you used a *iexplore browser string; this is almost surely inappropriate, so I'm changing it to *piiexplore...
16:19:11.296 INFO [11] org.openqa.selenium.server.BrowserSessionFactory - creating new remote session
16:19:11.656 INFO [11] org.openqa.selenium.server.BrowserSessionFactory - Allocated session 347c902e259040df8ea8f114531fd264 for http://localhost:8080/, launching...
16:19:11.656 INFO [11] org.openqa.selenium.server.browserlaunchers.WindowsProxyManager - Backing up registry settings...
16:19:11.968 WARN [11] org.mortbay.http.HttpConnection - POST /selenium-server/driver/ HTTP/1.1
org.openqa.selenium.server.browserlaunchers.WindowsUtils$WindowsRegistryException: Problem while managing the registry, OS Version '5.2', regVersion1 = false
at org.openqa.selenium.server.browserlaunchers.WindowsUtils.readBooleanRegistryValue(WindowsUtils.java:458)
at org.openqa.selenium.server.browserlaunchers.WindowsProxyManager$RegKey.backup(WindowsProxyManager.java:394)
at org.openqa.selenium.server.browserlaunchers.WindowsProxyManager$RegKey.access$000(WindowsProxyManager.java:356)
at org.openqa.selenium.server.browserlaunchers.WindowsProxyManager.backupRegistrySettings(WindowsProxyManager.java:231)
at org.openqa.selenium.server.browserlaunchers.InternetExplorerCustomProxyLauncher.launch(InternetExplorerCustomProxyLauncher.java:78)
at org.openqa.selenium.server.browserlaunchers.AbstractBrowserLauncher.launchRemoteSession(AbstractBrowserLauncher.java:26)
at org.openqa.selenium.server.BrowserSessionFactory.createNewRemoteSession(BrowserSessionFactory.java:312)
at org.openqa.selenium.server.BrowserSessionFactory.getNewBrowserSession(BrowserSessionFactory.java:113)
at org.openqa.selenium.server.BrowserSessionFactory.getNewBrowserSession(BrowserSessionFactory.java:79)
at org.openqa.selenium.server.SeleniumDriverResourceHandler.getNewBrowserSession(SeleniumDriverResourceHandler.java:635)
at org.openqa.selenium.server.SeleniumDriverResourceHandler.doCommand(SeleniumDriverResourceHandler.java:392)
at org.openqa.selenium.server.SeleniumDriverResourceHandler.handleCommandRequest(SeleniumDriverResourceHandler.java:370)
at org.openqa.selenium.server.SeleniumDriverResourceHandler.handle(SeleniumDriverResourceHandler.java:117)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1530)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1482)
at org.mortbay.http.HttpServer.service(HttpServer.java:909)
at org.mortbay.http.HttpConnection.service(HttpConnection.java:816)
at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:982)
at org.mortbay.http.HttpConnection.handle(HttpConnection.java:833)
at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:244)
at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)
Caused by: java.lang.RuntimeException: 1601 was not either 0 or 1: 257
at org.openqa.selenium.server.browserlaunchers.WindowsUtils$WindowsRegistryException.<init>(WindowsUtils.java:647)
... 22 more
16:19:11.968 DEBUG [11] org.mortbay.http.HttpConnection - RESPONSE:
HTTP/1.1 500 Internal Server Error
Date: Tue, 15 Jul 2008 14:19:11 GMT
Server: Jetty/5.1.x (Windows 2003/5.2 x86 java/1.5.0_11
Connection: close

I looked with regedit at the corresponding registry-key (HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3) and found:
1601 - REG_DWORD - 0x00000101 (257)

I looked into WindowsUtils.java and found the corresponding code:
public static boolean readBooleanRegistryValue(String key) {
    RegKeyValue r = new RegKeyValue(key);
int value = readIntRegistryValue(key);
    if (0 == value) return false;
    if (1 == value) return true;
    throw new WindowsRegistryException(r.value + " was not either 0 or 1: " + value);
}

In IE7 the security popup "you are sending... [] never ask again [yes] [no]" popped up when I tried to send data over the internet. When I checked the checkbox, the value in the registry was "0". I have now found a workaround, but I think it would be great, when the browserlauncher would consider the case, that the mentioned registry-key has the value 257, also.