Display count function output as letter value instead

I would like to output a letter instead of a number when performing a count
for a specific element.

For example, the code snippet:

<xsl:template match="//SelfStudy" mode="toc">
            <fo:block xsl:use-attribute-sets="TOC1">
                  <xsl:text>Self Study&#160;</xsl:text>
                              <xsl:value-of select="
count(preceding::SelfStudy)+1"/>
                              <xsl:text>&#160;-&#160;</xsl:text>
                              <xsl:value-of select="../../CuMetadata/Title
"/>

                  <fo:block xsl:use-attribute-sets="TOCLeaderSpacing">
                        <fo:leader xsl:use-attribute-sets="MediumLeader"/>
                  </fo:block>
            </fo:block>
            <xsl:apply-templates select="
SelfStudyContent/SelfStudyOverview/Body  |
SelfStudyReuse/SelfStudyReference | SelfStudyReuse/SelfStudyConcept |
SelfStudyReuse/SelfStudyConcept/CuInline/ContentUnit/CuContent/Concept/ConceptBody/subcontent/subheading
 | SelfStudyReuse/SelfStudyGWT |
SelfStudyReuse/SelfStudyGWT/CuInline/ContentUnit/CuContent/GuidedWalkThrough/Instructions/ConceptReview/ConceptReviewTitle
 |
SelfStudyReuseSelfStudyGWT/CuInline/ContentUnit/CuContent/GuidedWalkThrough/Instructions/SubInstruction/gwtSubHeading
" mode="toc"/>
</xsl:template>

would produce the following:
   SelfStudy 1 - Title
   SelfStudy 2 - Title
   SelfStudy 3 - Title
   ...

However, I would like it to output as follows:
   SelfStudy A - Title
   SelfStudy B - Title
   SelfStudy C - Title

How do I get the count to output as a letter value instead of a number
value?

Thanks for your help! Sharon
_______________________________
Sharon Goldner Harris
Knowledge Management Evangelist
Ultimate Software Group
704-660-6482

Confidentiality Note: This e-mail message and any attachments to it are
intended only for the named recipients and may contain legally privileged
and/or confidential information. If you are not one of the intended
recipients, do not duplicate or forward this e-mail message.