Escaping for use in URLs

I am looking for a way in XSL to escape text so that it can be added to
a URL.

An Example:

XML
<users>
<username>ed billings</username>
</users>

XSL

<a href="search.jsp?user={user/username}">

or

<a>
<xsl:attribute name="href">search.jsp?user=<xsl:value-of
select="user/username"/>
</xsl:attribute>
</a>

The problem with this scenerio is that the URL ends up looking like:

search.jsp?user=ed billings

instead of:

search.jsp?user=ed+billings


In javascript . . . this is very easy to do . . . .

Does anybody have any suggeestions.

Thanks!

ed billings

begin:vcard 
n:billings;ed
tel;work:312/234-2343
x-mozilla-html:TRUE
org:bank of america;web services
version:2.1
email;internet:edbi@xxxxxxx
title:web designer
adr;quoted-printable:;;233 south wacker dr.=0D=0Asuite 2800;chicago;il;60606;USA
note;quoted-printable:. . . =0D=0A=0D=0A" . . . whatever . . ."=0D=0A=0D=0A . . .
fn:ed billings
end:vcard