Existem várias maneiras de fazer isso:
Em httpd.conf (não em um arquivo .htaccess ):
RewriteEngine on
RewriteBase /
RewriteMap lowercase int:tolower
RewriteCond $1 [A-Z]
RewriteRule ^/?(.*)$ /${lowercase:$1} [R=301,L]
Ou em .htaccess (YMMV com desempenho) - observe que S=28 significa ignorar as 28 regras a seguir (conforme Documentação do Apache ):
RewriteEngine On
RewriteBase /
# If there are caps, set HASCAPS to true and skip next rule
RewriteRule [A-Z] - [E=HASCAPS:TRUE,S=1]
# Skip this entire section if no uppercase letters in requested URL
RewriteRule ![A-Z] - [S=28]
# Replace single occurance of CAP with cap, then process next Rule.
RewriteRule ^([^A]*)A(.*)$ $1a$2
RewriteRule ^([^B]*)B(.*)$ $1b$2
RewriteRule ^([^C]*)C(.*)$ $1c$2
RewriteRule ^([^D]*)D(.*)$ $1d$2
RewriteRule ^([^E]*)E(.*)$ $1e$2
RewriteRule ^([^F]*)F(.*)$ $1f$2
RewriteRule ^([^G]*)G(.*)$ $1g$2
RewriteRule ^([^H]*)H(.*)$ $1h$2
RewriteRule ^([^I]*)I(.*)$ $1i$2
RewriteRule ^([^J]*)J(.*)$ $1j$2
RewriteRule ^([^K]*)K(.*)$ $1k$2
RewriteRule ^([^L]*)L(.*)$ $1l$2
RewriteRule ^([^M]*)M(.*)$ $1m$2
RewriteRule ^([^N]*)N(.*)$ $1n$2
RewriteRule ^([^O]*)O(.*)$ $1o$2
RewriteRule ^([^P]*)P(.*)$ $1p$2
RewriteRule ^([^Q]*)Q(.*)$ $1q$2
RewriteRule ^([^R]*)R(.*)$ $1r$2
RewriteRule ^([^S]*)S(.*)$ $1s$2
RewriteRule ^([^T]*)T(.*)$ $1t$2
RewriteRule ^([^U]*)U(.*)$ $1u$2
RewriteRule ^([^V]*)V(.*)$ $1v$2
RewriteRule ^([^W]*)W(.*)$ $1w$2
RewriteRule ^([^X]*)X(.*)$ $1x$2
RewriteRule ^([^Y]*)Y(.*)$ $1y$2
RewriteRule ^([^Z]*)Z(.*)$ $1z$2
# If there are any uppercase letters, restart at very first RewriteRule in file.
RewriteRule [A-Z] - [N]
RewriteCond %{ENV:HASCAPS} TRUE
RewriteRule ^/?(.*) /$1 [R=301,L]
Ou usando mod_spelling (sua configuração sugere que você está usando o Windows para que o YMMV também esteja aqui):
<IfModule mod_speling.c>
CheckCaseOnly On
CheckSpelling On
</IfModule>
Fonte: link