hi.
apache version 1.3.33.
a simple test, create big file:
dd if=/dev/zero of=big_file_3gb_test.bin bs=1024 count=$[1024*3090]
for a small file:
oraserv:/srv/www/tomcat5/base/webapps # HEAD http://localhost/tomcat-power.gif
200 OK
Connection: close
Date: Tue, 30 Aug 2005 11:43:14 GMT
ETag: W/"2324-1103319358000"
Server: Apache/1.3.33 (Linux/SuSE) mod_ssl/2.8.22 OpenSSL/0.9.7d PHP/5.0.4 
mod_jk/1.2.10
Content-Length: 2324
Content-Type: image/gif
Last-Modified: Fri, 17 Dec 2004 21:35:58 GMT
Client-Date: Tue, 30 Aug 2005 11:43:14 GMT
Client-Peer: 127.0.0.1:80
Client-Response-Num: 1

next,
oraserv:/srv/www/tomcat5/base/webapps # HEAD http://localhost/big_file_3gb_test.
txt
200 OK
Connection: close
Date: Tue, 30 Aug 2005 11:43:06 GMT
ETag: W/"3240099840-1125400325000"
Server: Apache/1.3.33 (Linux/SuSE) mod_ssl/2.8.22 OpenSSL/0.9.7d PHP/5.0.4 
mod_jk/1.2.10
Content-Type: text/plain
Last-Modified: Tue, 30 Aug 2005 11:12:05 GMT
Client-Date: Tue, 30 Aug 2005 11:43:06 GMT
Client-Peer: 127.0.0.1:80
Client-Response-Num: 1

no Content-Length is in returned headers for 3Gb size file. 
If i use GET request, it's same, for small file Content-Length is returned and 
for big file is not.

Content-Length header is very important, since it possible to resume downloads 
based on this.
Any comments on this? Thanks.